Heat oven to 425°F Spray a large rimmed baking sheet with cooking spray; set aside.
Combine crushed crackers, Parmesan, and pepper in a shallow dish; set aside.
Slice each chicken breast in half horizontally, so you have 8 pieces total. Pound each chicken piece between two sheets of plastic wrap until very thin, about 1/4" thick.
Coat chicken in butter, then dredge in cracker mixture, pressing crumbs firmly onto each piece. Lay chicken in a single layer on the baking sheet. Bake 12 minutes or until golden and cooked through.