Heat oven to 180C. Heat 1 tbsp oil from the olives in an ovenproof pan. tip in teh onion and stir well then leave to cook for a minute or two. Add the tomatoes and some salt and pepper. Bring to the boil, then add the drianed olives.
STEP 2
Put the fish, skin side down, onto the sauce and drizzle with more oil from the olives. bake uncovered in the oven for 15 mins and serve with baked potatoes.