Peel garlic and cut into thin slices. Peel, core and cut tomatoes into small pieces. Cut the peppers into thin strips.
Divide fish fillet into portions, season with salt and pepper. Heat oil in a nonstick skillet and sauté garlic stirring briefly. Add peppers and tomatoes and season with salt, pepper and oregano. Simmer all covered 10 minutes to a sauce.
Put fish fillet upon the vegetables and cook covered over low heat 7 minutes.