Cut grapefruit in half crosswise; remove seeds, and loosen sections.
Place grapefruit, cut side up, on rack of a broiler pan.
Sprinkle each grapefruit half with 1/4 teaspoon sugar.
Spread 1 tablespoon strawberry spread over each half.
Broil 5 1/2 inches from heat (with electric oven door partially opened) 6 minutes or until thoroughly heated and sugar melts.
Top each half with 1 tablespoon yogurt.