Serves 6
Preheat your grill. Combine the olive oil, vinegar, basil, garlic, salt and pepper in a small bowl. Stir to combine.
Place the tomatoes, cut-side down, on the grill. Grill until they start to bubble and blister, 4-5 minutes. Carefully turn the tomatoes over and grill for 2 minutes more.
Remove the tomatoes from the heat. Place cut-side up in a baking dish. Spoon the marinade over the tomatoes while they are still hot. Set the dish aside for at least one hour, or cover and refrigerate for up to 5 days.