Arrange tomatoes, cut side up, on rimmed baking sheet. Sprinkle with salt and pepper, then 1 1/2 Tablespoons each oregano and thyme leaves. Drizzle with 3 Tablespoons oil.
Prepare barbeque (medium-high heat). Brush grill with oil. Place tomatoes, cut side up, on rack. Cook until bottoms are charred 3-4 minutes. Turn tomatoes over and grill just to sear, about 1 minute. Turn cut side up onto platter. Sprinkle with 1/2 tablespoon each oregano and thyme, then drizzle with more oil, if desired. Serve warm.