8 (1/4-inch-thick) tomato slices from medium to large tomatoes
1/4 teaspoon freshly ground black pepper
1/8 teaspoon salt Directions: Combine mayonnaise and pesto in a bowl, stirring well.
Arrange bread in a single layer on a cutting board. Spread about 2 teaspoons pesto mixture over each bread slice. Add one slice of cheese to each of 4 pieces of bread. Arrange 1/4 cup arugula and 2 tomato slices over cheese mixture; sprinkle tomato slices evenly with pepper and salt. Spread about 1 1/2 teaspoons of remaining pesto mixture evenly over one side of each remaining bread slice; place 1 slice, pesto-side down, on top of each sandwich. Spray pan with cooking spray. Grill sandwiches about 2 minutes on each side over medium heat.