One-pot fish with tomatoes and olives

This is a wonderfully simple and healthy dish for a low-fat supper - you can cook it for five minutes then leave just leave it in the oven while you get on with something else. The flavours are also infinitely variable - add whatever you like to make it more substantial (see below) or keep it simpe and serve with rice or couscous.

Ingredients

1 large onion, roughly chopped
400g can chopped tomatoes
6 oz black olives
4 boneless white fish fillets
pesto
variants: sun-dried tomatoes, capers, artichoke hearts...

Method

1. Preheat the oven to 200° C (fan 180° C)
   
2. Heat 1 tbsp of oil in an ovenproof pan (use the oil from the olives or sun-dried tomatoes if using). Tip in the onions and stir well, leave to cook for a minute or two.
   
3. Stir in the tomatoes and some salt and pepper. (If you are wanting a more substantial dish, or if your pan is shallow but quite wide, you may wish to use two tins of tomatoes.) Bring to the boil, then add the drained olives and any 'variant' ingredients.
   
4. Put the fish, skin-side down, onto the sauce and drizzle the fillets with pesto.
   
5. Bake uncovered for 15 mins until the fish is cooked. Serve straight from the pan.