Slice your onion into rings and peppers into strips. Fry them gently for around 5-8 mins until soft.
Place half the peppers and onion mixture into a shallow baking dish then put your raw snapper fillets on top. Then put the rest of the veggies around the fish and put a sprig of rosemary on each fillet. Brush the top of each fillet with a little more oil then season the whole dish with salt and pepper.
Cover the dish with foil and bake for 15 minutes.
After 10 minutes of baking, cut a ciabatta loaf down the middle so you have 2 long strips. Melt your butter in a griddle pan. Rub each bread side with a raw clove of garlic then fry it for around 5 minutes until toasted.
When the fish is ready, squeeze a little lemon on top then serve with the buttery, garlicky ciabatta on the side.