GRILL DIRECTIONS: Heat grill. Cut four 12-inch-square pieces of heavy-duty foil. If desired, peel potatoes. Make 4 or 5 crosswise cuts in each potato, cutting to but not through bottom. Spread margarine between slices.
Cut each onion into 8 to 10 thin slices. Insert onion slice into each potato slice. Sprinkle with salt, pepper and paprika. Place each potato on square of foil. Wrap each packet securely using double-fold seals, allowing room for heat expansion.
When ready to grill, place packets, seam side up, on gas grill over medium-high heat or on charcoal grill 4 to 6 inches from medium-high coals. Cook 40 to 50 minutes or until vegetables are tender, turning occasionally. Open packets carefully to allow hot steam to escape.