CUT pork into 1-inch-thick slices. Place pork between two pieces of plastic wrap. Flatten to 1/4-inch thickness using meat mallet or rolling pin. Season with salt and ground black pepper, if desired.
HEAT oil in large, nonstick skillet over medium-high heat. Add half of the pork; cook on each side for 2 minutes or until browned and cooked through. Remove from skillet; set aside and keep warm. Repeat with remaining pork.
REDUCE heat to low. Add evaporated milk; stir to loosen brown bits from bottom of skillet. Stir in mustard and green onions. Return pork to skillet. Cook for 1 to 2 minutes or until sauce is slightly thickened, turning pork to coat with sauce.