Grilled Heirloom Tomato and Mozzarella Sandwiches with Green Heirloom Tomato Gazpacho

Name: Grilled Heirloom Tomato and Mozzarella Sandwiches with Green Heirloom Tomato Gazpacho
Ingredients: 1 pound ripe green heirloom tomatoes, cored, cut into large chunks; 1 6-inch piece unpeeled English hothouse cucumber, diced; 1/2 cup chopped onion; 1/2 cup chopped celery; 1/2 cup salted roasted Marcona almonds; 2 tablespoons extra-virgin olive oil; 2 large garlic cloves, peeled; 1 tablespoon Champagne vinegar or other white wine vinegar; 1 teaspoon (or more) coarse kosher salt; 8 1/3-inch-thick slices brioche or challah, trimmed to 5x3 inches; 1 8-ounce package smoked mozzarella cheese, cut into 1-inch-wide by 1/8-inch-thick slices; 2 large heirloom tomatoes (preferably Brandywine), cut into 1/4-inch slices; 1/4 cup (1/2 stick) butter