The idea of baking a citrus fruit is pretty cool and, for me, probably the only way to get this particular food to be palatable.  I can't help but feel like grapefruit should have been left to cottage-cheese loving dieters in the 1980's, but it is good for you, so a little accessorizing-- like in this recipe-- is well worth the effort.   This is straight from the Fanny Farmer Cookbook, with some small adjustments.

By the way, the cinnamon totally makes it.

Prep Time: 2 Minutes
Cooking Time:  15 Minutes
Yield:  4 Servings
Ingredients:
2 Large Grapefruit
1 Tsp Organic Butter or Soy Butter, softened
1 Tsp Agave Nectar, Honey or Maple Syrup
A Few Pinches of Cinnamon

Preheat oven to 450 degrees.  Cut each grapefruit in half crosswise and use a sharp knife to loosen each section.  Divide the butter among the four halves, spreading over the cut surface.  Drizzle with sweetener, dividing it among the four halves.  Place in a baking pan or directly on the oven rack, cut side up, and bake for 15 minutes.  Sprinke with cinnamon and serve.