Dredge fish in flour and place in a baking pan. Melt butter and simmer onion, celery, and green pepper for 15 minutes. Add the remaining ingredients and simmer until celery is tender. Remove lemon slices and bay leaves.
Optional: press sauce through a food grinder or potato ricer.
Pour sauce around the fish and bake at 350°F until fish is tender, 15-20 minutes. Serve with rice.
