I found the recipe for this yummy-ness at Williams-Sonoma and made a couple of adjustments...
What You'll Need: 1 grapefruit - 1/4 c of rapadura (or brown sugar) - 1 T butter, melted - 1/2 t cinnamon
What To Do: Cut a grapefruit in half and section pieces. Mix rapadura/brown sugar with butter and cinnamon and pour over the top of each half.
Place on a baking sheet about 4 inches from the broiler and heat for 2-3 minutes until everything's uniformly bubbly.