Clean and dry the fish and place them on a buttered baking dish. Peel the lemon and cut into fine slices, while removing the seeds. Peel and seed the tomatoes, and cut into small pieces. Brown the onion in the butter. Add the finely sliced green pepper, the tomato, the bay leaf and salt. Cook for 5 minutes. Put the dill and thin lemon slices over the fish, and pour the sauce over. Cover and place in a warm oven for 10 minutes.