Preheat the oven to 180ºC/350°F/Gas 4. Put the tomatoes and peppers in a small roasting tray. Drizzle with the balsamic vinegar and half the olive oil. Bake for 5 minutes until the tomatoes are softening.
Remove the roasting tray from the oven. Nestle the cod fillet among the peppers and tomatoes and drizzle with the remaining oil and the lemon juice. Scatter with the basil leaves and bake for a further 15 minutes until the fish is cooked through.
Serve hot or put the fish and vegetables in a food processor and process to form a purée if you're making this for a baby.
Recipe by Grace Cheetham at https://www.gracecheetham.com/gluten-free-dairy-free-mediteranean-baked-cod