In a small saucepan, cook chopped onion, crushed garlic clove, and chili powder in butter until tender. Stir in tomato sauce, vinegar, honey, salt, and pepper; bring to boiling, stirring constantly. Boil for 5 minutes, or until slightly thickened.
Meanwhile, pat dry flank steak and score diagonally into diamonds on both sides. Brush with sauce; grill over medium coals for 7 minutes until done, brushing occasionally with the remaining sauce.
Servings: 4