In a medium saucepan cook broccoli and sweet pepper in a small amount of boiling, lightly salted water about 8 minutes or until broccoli is crisp-tender; drain. Return broccoli mixture to saucepan; cover and keep warm.
Meanwhile, for sauce, in a small saucepan cook onion and garlic in hot margarine until onion is tender. Stir in cornstarch. Add orange juice and mustard. Cook and stir until thickened and bubbly. Cook and stir for 2 minutes more. Pour the sauce over broccoli mixture; toss gently to coat. Makes 6 servings.