Melt margarine in a large Dutch oven over medium-high heat. Add onion; sauté 7 minutes. Stir in sugar and pepper. Cover, reduce heat to medium-low, and cook 20 minutes or until golden, stirring frequently. Remove onion mixture from pan; set aside.
Place pan coated with cooking spray over medium-high heat until hot. Gradually add turnip greens, and cook 10 minutes or until wilted, stirring frequently. Add onion mixture to turnip greens; stir gently. Sprinkle with hot pepper sauce, if desired. Serve immediately.