Melt margarine in a large Dutch oven over medium-high heat.
Add onion; saut 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.