Place a wire cooling rack on a rimmed baking sheet and place in the oven; preheat to 450º.
Place pork chops on a large cutting board. Cover with plastic wrap and pound with the smooth side of a meat mallet to about 1/4" thickness. Sprinkle with pepper and salt. Place flour, egg and pretzels in three separate shallow dishes. Dredge the cutlets in flour, shaking off excess, then dip in egg, letting excess drip off, then press into pretzels. Generously coat one side of the cutlets with cooking spray.
Remove the heated pan from the oven. Put the cutlets, sprayed-side down, on the rack. Coat the second side generously with cooking spray. Bake until golden brown, 8 to 12 minutes.
Combine the yogurt and mustard in a small bowl. Serve with the pork.