Heat a grill to medium-high heat. In a small bowl, combine garlic, lemon juice, lemon zest, parsley, oregano, 2 tablespoons olive oil and salt and pepper.
Halve the tomatoes crosswise and brush cut sides with remaining 2 tablespoons of olive oil. Place them, cut side down, onto grill. Grill for 4 minutes. Flip the tomatoes and grill until skins begin to char, 3 minutes. Transfer to serving plate, cut sides up, and drizzle the lemon-herb mixture over top. Serve warm.