Avocado-White Cheddar-Tomato Grilled Cheese Recipe

California avocado, mashed 1 tsp. lemon juice 1/2 tsp. kosher salt 4 slices of bread of your choice (I like sourdough or whole wheat) 4 ounces sharp white cheddar cheese, divided (I love Cabot!) 8-10 grape tomatoes, sliced in half