Heat grill. Brush cut sides of tomatoes with 2 teaspoons oil and grill, cut side down, without turning, until charred, about 10 minutes. Remove from grill using spatula, transfer to cutting board, and chop. Set aside. Toss shrimp with remaining 1 teaspoon olive oil and sprinkle with 1/4 teaspoon salt. Grill, turning once, until cooked through, about 6 minutes. Set aside.