Wash and drain the fish fillets, shrimp and squid. Place it on a paper towel and drain excess water. Cut the fish fillets into cubes and flour them. Prepare the shrimp by cutting them whole and the squid in half.
Melt the butter in the casserole dish, add the lightly floured fish and sauté for 2-3 minutes. Chop the red onion, add it and sauté for a few more minutes. Then add the diced peppers, shrimp, squid and peeled and diced tomatoes.
Season with salt and pepper and cook over low heat with the lid closed for 10-15 minutes. Remove from the stove, sprinkle finely chopped fresh coriander on top and serve hot.
