The recipe Cut 450g of assorted tomatoes in half and put them in a mixing bowl. Peel and very finely chop 2 fresh, young cloves of garlic and add them to the tomatoes. Remove the leaves from a handful of thyme (6 bushy little sprigs will do), then toss them with the tomatoes and garlic, 3 tbsp of olive oil and a fulsome pinch of salt. Open a 400g tin of borlotti beans and tip the entire contents into a deep baking dish, then season with black pepper. Drain a large tin of sustainable tuna and put the tuna in the middle of the beans. Scatter the tomatoes and their dressing around the fish, then trickle over a little more olive oil, tuck in a few sprigs of rosemary or oregano if you happen to have some, then bake for 25-30 minutes. Serves 2 The trick This is one of those occasions when dinner is more about opening cans than cooking. No matter, it gives the impression of one of those recipes that has been simmering quietly in the oven for hours. By all means eat it straight from the oven, but this dish seems better for being eaten warm rather than piping hot, so give it a few minutes in which to relax. I like to serve bread with this supper, maybe ciabatta or a baguette, thinly sliced, toasted and drenched in the juices from the pot. The twist Tomatoes aside, this is very much a store-cupboard supper. Use canned chopped tomatoes if that is what you have. Cannellini, flageolet or haricot beans will work instead of the borlotti. If tuna isn’t your thing, you could turn this into a slightly different, and indeed vegetarian, dish by using a jar of preserved artichoke hearts in its place – in which case I would add some green olives, too. The Observer aims to publish recipes for fish rated as sustainable by the Marine Conservation Society’s Good Fish Guide Follow Nigel on Twitter @NigelSlater