Brush the tomato halves olive oil. Season them with salt and pepper, then sprinkle the garlic and chopped sage over them. Press a whole sage leaf in the center of the cut side of each tomato half. Set any leftover olive oil aside.
Get to grilling! Get whatever grill you have to medium heat, oiling the cooking surface if appropriate. Cook until soft, generally about 5 minutes, but depending on the grill, less or more. Take your tomatoes off the grill, drizzle with olive oil, serve!