Heat your grill to high. Brush the fish with oil and season both sides of the fish with the salt and pepper. Place the fish on the grill, and grill for 3 to 4 minutes or until golden brown and slightly charred. Turn the fish over and continue grilling, for 3 to 4 minutes for medium doneness. Remove the fish from the grill and let rest 5 minutes. Drizzle mojo over snapper and serve with grapefruit slices on the side.
For the grapefruit-thyme mojo:
Combine all of the ingredients in a blender and blend until smooth.