Slice steak thinly in short crosswise pieces. Heat butter in skillet and add garlic, salt and pepper. Add beef and brown on both sides. Add soy sauce and sugar; cover and simmer for 5 minutes. Add rinsed sprouts, tomatoes and green peppers; cover and simmer 5 minutes. Dissolve corn starch in water and stir in. Stir until sauce thickens. Sprinkle with onions and serve on rice.