So, in the spirit of trying to come up with healthier versions of some American dishes, came this...
Other than 'collard greens', my knowledge of traditional dishes involving green vegetables from the USA was pretty limited. And it turns out that, well... there just aren't that many? Which was confirmed by a couple of people I know from the states. So this dish was vaguely 'inspired', if I can call it that, by an Ina Garten spinach gratin dish.
We served it alongside the American-style Pot Roast Brisket of Beef I made, along with some Southern-style Green Beans with Bacon, and I'm guessing it would go with poultry and pork quite well too. You could probably bump it up to something more significant as a larger part of a meal if you're vegetarian, and serve with some balsamic-roasted tomatoes or roasted vegetables.
This serves six as a small side dish, at 60 calories per serving.
In her recipe, Ina suggests using frozen chopped spinach, so I went with that as I had some in the freezer. She also adds lots of butter and cream to it, and tops with lots of Parmesan cheese, but I decided I'd use a light cream cheese to give it a 'creamy' base instead, and also add some sliced, lightly sauteed mushrooms to give some texture to it as well, with a little garlic and just use a little Parmesan so it didn't overpower whatever it was served with. I think it would also be nice with a bit of a crunch to it, maybe some roughly chopped and toasted pine nuts sprinkled over the top, or a savoury crumb or crumble, maybe with some crispy bacon or pancetta...and better with fresh spinach, just wilted and lightly chopped then mixed with the other ingredients and quickly flashed under a very hot grill (broiler) to lightly brown the top. But I'll reproduce it as I cooked it and leave the variations to you.
300g chopped frozen spinach, defrosted 
150g mushrooms (e.g. chestnut), sliced 
1 onion (120g), diced 
2 garlic cloves, crushed 
1 tsp (5g) butter 
60g light cream cheese (e.g. Philadelphia Light) 
A little nutmeg, freshly grated 
Salt and freshly ground black pepper 
20g Parmesan cheese, finely grated (in two x 10g - for vegetarians look out for vegetarian Italian style cheese, e.g. from Ocado) 
Pre-heat the oven to gas mark 7 / 220C (200C Fan) / 425F. Sautee the onions in the butter over a low heat, for about five minutes until softened. Add the mushrooms and a pinch of salt and cook for another couple of minutes until they are just starting to soften a little and release some of their juices, then add the garlic and continue to cook for another couple of minutes until they are just tender.
Give the cream cheese a quick stir with a fork, then add it to the pan with a little grating of nutmeg and a good grinding of black pepper. Stir into the mushrooms, then add 10g of the Parmesan cheese, and the defrosted spinach and then stir for a minute or two until just heated through. Give it a quick taste for seasoning, and add further salt and pepper if required.
Spoon into an ovenproof dish, and scatter the rest of the grated Parmesan cheese on the top (feel free to use more if you're not counting calories). Put into the oven for about 20 minutes until the top is just starting to turn golden brown in places, and serve immediately.