Spread 1 1/2 teaspoons mustard over each bread slice. Layer each of the 4 slices with 1 ounce turkey, 2 tomato slices, 1 cheese slice, 1 tablespoon bacon bits, and a dash of pepper. Top with remaining bread slices. Heat a large nonstick skillet coated with cooking spray over medium heat. Place 2 sandwiches in the pan; cook 2 minutes on each side or until toasted. Repeat procedure with remaining sandwiches. Cut each sandwich in half.