Mix 1-1/3 cup grated sharp cheddar cheese and 2/3 cups Monterey jack cheese with 2 tablespoons mayonnaise, 2 tablespoons jarred pimentos drained and chopped, 2 teaspoon minced onions, 1/2 teaspoon hot pepper sauce, and 1/4 teaspoon pepper. Layer each sandwich with cheese mixture and 2 thin sliced tomatoes. Grill until golden brown.