- Preheat the oven to 190°C / fan 170°C / Gas Mark 5.
- Heat 2 tbsp of the olive oil in a frying pan over a medium heat. Saute the red onions, tomatoes and garlic for 2-3 minutes until the tomatoes have softened.
- Spoon into an oven proof dish, season with black pepper and place the smoked haddock fillets on top.
- Tear the mozzarella evenly over the smoked haddock and sprinkle with the Cheddar cheese.
- Place the rosemary sprigs on top and drizzle with the remaining olive oil.
- Bake in the oven for 20 minutes until golden brown.
- Serve with chunks of crusty white bread.