Place chicken between 2 sheets of plastic wrap; pound to 1/4-inch thickness. Sprinkle chicken evenly with pepper and salt.
Heat a skillet over medium heat. Add panko; cook 2 minutes or until toasted, stirring often. Remove from heat. Place flour in a dish. Combine 1 tablespoon water and egg in a bowl; lightly beat. Pour egg mixture into a dish. Combine panko, 2 tablespoons cheese, thyme, and garlic in a dish.
Working with 1 piece of chicken at a time, dredge in flour. Dip in egg mixture; dredge in panko mixture. Top with 1 pancetta slice and 2 tablespoons cheese. Roll up; secure with a toothpick. Place roll, seam side down, on a wire rack coated with cooking spray. Place rack on a baking sheet. Repeat procedure with remaining ingredients. Bake at 350° for 25 minutes or until chicken is done.