So, I bought these 'chayotes' a week ago, and had never cooked or eaten one before...
Turns out I've been missing out! They're very versatile, and can be eaten raw (they have a taste a little like a combination of raw courgette and melon, and a crisp texture a bit like an asian pear - more here in my blog about chayotes) or cooked, and they're low in calories too (only 19 calories per 100g).
So anyway, moving on from the ingredients, to the soup - this is a delicious, spicy Louisiana soup which tastes far more indulgent than it really is - blending half of the chayotes after cooking (but before adding the shrimp/prawns) gives it a nice rich thickness, a bit like when you blend potato into a soup. This gives you a nice hearty portion too, which is delicious on its own!
Serves two, 134 calories per serving (including maximum amounts of all ingredients).
1 chayote/mirliton, peeled and cut into 1cm dice (200g flesh) (or substitute courgette/zucchini, no need to peel) 
100g your favourite prawns/shrimp*, peeled and de-veined 
1 tsp butter 
1/2 medium onion, finely diced (50g) 
1/2 celery stick, finely diced (30g) 
1/2 small green pepper, finely diced (40g) 
1 clove garlic, finely chopped 
1 bay leaf (fresh or frozen, if possible)
1-2 level tsp Cajun seasoning, to taste (2 tsp is medium to hot, Schwartz or similar is fine if you want to use a blend) [5-10]
1 tbsp tomato puree 
1-2tsp lemon juice, to taste [1-2]
300ml chicken stock (I use Knorr Touch of Taste Chicken Boullion, taste your stock once you've made it up to check it's not too salty, before you add it to your soup - remember, you can add salt, but not take it away!) 
1 tbsp chopped fresh parsley or 1 tsp dried (you could substitute coriander/cilantro, but it's not authentic, although it does taste really good with this!) - reserve a few leaves to garnish 
Optional: 1-2 level tbsp Greek yoghurt, to taste, beaten with a fork until smooth (or you could use double cream if you're feeling indulgent! Just up the calorie count accordingly. For Paleo, you could use coconut milk) [14-29]
Salt and freshly ground black pepper to taste 
Take a heavy-based, non-stick pan and place over a low to medium heat. Add the butter and swirl around, then add the onions, pepper and celery and sautee for 3 to 5 minutes until softened. Add the chayote, and
cook for a further two minutes, then add the garlic and bay (pushing the bay to the bottom of the pan, so it releases its oils) stirring for another 30 seconds. Finally, add the Cajun spice, and stir in for another 30 seconds (you might want the extractor fan on for this bit!) until fragrant, making sure your garlic doesn't catch or burn.
Providing your chayote is now tender, with a ladle carefully remove
about half of the soup into a blender/food processor, and quickly blitz until smooth then add back to the soup. Give it a good stir to incorporate it, and see whether the thickness is too your liking (if it seems too thick, add a little hot water to thin it out). Give your soup an initial taste, and add more lemon juice, and salt and pepper to taste (you may not need to add any salt if you've used a bought Cajun spice blend, as they mostly contain salt, whereas my blend doesn't).
Take off the heat, then stir in the fresh parsley and 1 tbsp Greek yoghurt (or cream) if using, taste, and add the other tbsp yoghurt (or more, to taste!). Serve immediately, garnished with the reserved leaves.
Re. prawns/shrimp: I used Sainsbury's 'Taste the Difference' frozen cooked and peeled Jumbo king prawns, defrosted* and cut in half lengthways. You can use cooked or raw, fresh or frozen (just de-frost them before using). Just make sure any black 'veins' are cut out from the back of the prawn - see this video if you're not sure how. If you add cooked prawns, you just literally need to warm them through, whereas with raw prawns, you need to cook until they have changed colour to pink, curled, and are cooked all the way through. Cooking times will vary depending on the size of the prawns you use. You can chop them into bite-size pieces if you're using larger prawns, so that they're easier to eat. I cut mine down the middle lengthways, so they still looked prawn shaped, but were more bite-sized.