In a small bowl coat 4 tomato slices evenly with cornmeal and season with salt. In a 10- to 12-inch heavy skillet heat 1/4 cup reserved bacon drippings over moderate heat until hot but not smoking and cook tomatoes until golden brown on both sides, about 5 minutes, transferring them as cooked to paper towels to drain. Coat and cook remaining tomatoes in same manner, using additional drippings if necessary.
On a baking sheet broil one side of bread slices about 3 inches from heat until golden. Make sandwiches by layering, on untoasted sides of bread, mozzarella, basil, tomatoes, and bacon. Top with remaining bread slices, toasted sides up.