Coat a nonstick grill pan or sandwich press with cooking spray. Heat to medium.
Place 4 bread slices on a work surface. Spread each with tomato sauce. Divide the cheese among the four slices; fold the cheese to fit, if necessary. Spread the remaining bread slices with pesto and sprinkle with herbs. Place, pesto side down, on top of the cheese-topped bread slices.
Grill on the grill pan or in the sandwich press for 3 to 5 minutes or until cheese is melted (turn sandwiches on grill pan once during cooking).