Although it is a beautiful looking dish, it's actually incredibly simple to cook and plate up. You just add the ingredients for the broth to the bowl, with the mushrooms and spinach in the varoma and press go! If you would like to cook this without using a Thermomix, see here for my original recipe with a method on the hob. This serves two to four people (timings for both in method, and if you're counting calories, it's a mere 121 calories per person!).
Feel free to tweak this dish to suit you. I've converted this version to Thermomix with a dashi broth substitute I came up with for Japanese soups, as I am aware that most people won't be making their own dashi broth, and the majority of 'instant dashi' powders and concentrates you can buy contain MSG as an additive. MSG does actually occur naturally - the white residue you find on seaweed, i.e. Kombu (kelp, one of the two ingredients dashi is made from) is naturally occurring MSG but I don't think most people want to add it to their food, or include it in chemical form, although opinions are mixed. Also, I thought it might make a nice use of a light bone broth, for those who make them.
Anyway, I digress - if you'd like to make your own dashi stock, whether with a piece of kombu and bonito flakes, or the vegan version with kombu and dried shiitake mushrooms, my recipes are here. If you'd like to make the whole soup vegetarian (or vegan), you can do that too and top it with something other than crab (i.e. tofu, marinated tofu, soy and honey roasted squash, sesame-miso green beans etc.) and garnish it with snipped chives, finely sliced spring onions, or even some nutritional yeast flakes, for an umami-rich bonito flakes replacement. Food is fun and there to be played with, right?
Just in case you hadn't heard of it, an 'ohitashi' is a Japanese dish, consisting of a broth (e.g. dashi stock) containing seasonal ingredients, usually green-leafed vegetables. We don't really have a word or equivalent for it - it's that infamous soup/salad hybrid I spoke of in my welcome. It is served anywhere between warm in winter and chilled in the summer, when the ingredients are almost like having a spinach salad in a broth. You could choose to serve it hot, which is also delicious, as lukewarm soup is not to everyone’s taste! I must admit, I serve the broth and spinach hot, with the crab meat at room temperature on top of the spinach, then when you stir it all together it is nice and hot all the way through.
Serves two to four, 121 calories per serving. (Timings for two and four given in method). I have put ml/g to indicate with certain liquids you can choose whether you measure them into a jug etc. by volume (ml) before adding, or weigh them in (g). I'm not so great at remembering to press the button to weigh things, so tend to measure before adding liquids!!
Ingredients for four servings
(Halve for two servings)
240g white crabmeat, very good quality tinned is fine - one tin drained is usually 120g (fresh crabmeat for clean eating) 
300g baby spinach leaves 
300g mixed (oriental) mushrooms, e.g. shimeji, enoki or oyster mushrooms (or if you can’t get hold of any of these, just used small, sliced chestnut or button mushrooms) 
A sprinkling of bonito flakes*, or chopped chives or sliced spring onions to serve (or all three - optional) 
For the ohitashi broth
(Halve for two servings, except for the water - 1,100ml/g for four, but 600ml/g for two)
1.1 litres / 1,100g cold water (or 800ml/g cold dashi stock, light bone broth or chicken/vegetable stock plus 300ml/g cold water to make up to 1,100ml/g - see my blog on dashi stock if you want to know more about this - I've been really organised and posted the recipe for normal dashi broth as well as the vegan version, and the Western-based substitute! Also for notes re. gluten]
Chicken (or vegetable) stock concentrate/paste/powder/cubes to make up 800ml stock IF you're using water only, as above (e.g. two and a half 15ml tbsp of Knorr Touch of Taste Chicken Bouillon concentrate, or just under 2 stock cubes - the clearer the better, or you can strain after - check GF if appropriate) 
2 x 15ml tbsp oyster sauce (you can get vegetarian oyster sauce, widely available, most oyster sauces contain gluten, but there are gluten free, e.g. ASDA own brand, substitute coconut aminos for Paleo) 
2 tsp fish sauce (or vegetarians use an extra teaspoon of light soy/tamari sauce - for Paleo, Red Boat brand is suitable) 
3 dried shiitake mushrooms, rinsed (optional)
50ml/g tamari soy sauce (plus possible extra to taste OR light soy sauce is good if you don't need to be gluten free, or coconut aminos to suit your diet) 
50ml sake (or just add extra water - skip sake for clean eating/Paleo etc., and be careful if cooking gluten free as some involve barley in the process, safer to use dry sherry, or dry white wine if you're not sure of your brand) 
Clean the mushrooms of all dirt/grit, cut off the base (for the shimeji/enoki mushrooms) and separate the individual mushrooms, or if using oyster, then trim the stalks, and cut or tear the large ones into smaller strips, and slice any other mushrooms. Make sure all the mushrooms are evenly sized pieces/strips/slices and toss them into the bottom of the Varoma, making sure there are spaces for the steam to get through.
Wash and drain the spinach, and place in the Varoma tray on top of the mushrooms. I'm not going to lie to you - getting 300g in here is a bit like trying to get into the jeans you bought in November on January 2nd. You just need to lie it as flat as possible, then give it a good squish and put the lid on top. It's a tight fit!
Add all of the ingredients for the ohitashi broth to the Thermomix bowl (if you are using tinned crab, you can drain the juices into the broth for extra flavour when you open the tin), lock the lid onto it, put the varoma with the mushrooms, spinach (and lid!) on top, and cook at Varoma Temperature / Reverse Spoon / 19 minutes** / Speed 2 (**17 minutes if halving ingredients for two servings). Meanwhile, get your bowls ready for serving, if you want to use food rings, and chop any chives / spring onions if using.
Once cooked, if you just want the simple version, then fish out the shiitake mushrooms from the bowl (or strain through a seive), taste the broth and add extra soy sauce if required, and add the spinach, mushrooms and crabmeat to the broth, and serve, sprinkled with bonito flakes / chives / spring onions if desired.
See? It's not quite so pretty when you stir it all together, but it still tastes sensational!
*Bonito flakes are dried, smoked flakes of tuna, a traditional Japanese ingredient. The above is a link to a brand which I use from amazon, which I have been very happy with. You can view the product through this link, which is an affiliate link. If you choose to buy it, I will get a very small percentage of the proceeds, and you will pay no extra. Or if you have a decent oriental store near you, go and have a look there - but beware, they can be quite pricy!