Trim fat from pork. Cut the tenderloin crosswise into eight 3/4-inch-thick slices. Place each slice between 2 pieces of plastic wrap. Pound lightly with the flat side of a meat mallet to form 1/2-inch-thick medallions. Remove plastic wrap. Place medallions on a platter and sprinkle with seasoned pepper.
Coat an unheated large nonstick skillet with cooking spray. Place skillet over medium heat. Add pork medallions. Cook for about 3 minutes per side. Remove meat from skillet; cover with foil and keep warm.
In the same skillet, cook mushrooms for 3 minutes, stirring occasionally, to brown slightly. Carefully add broth, mustard and salt. Bring to boiling; reduce heat. Simmer, uncovered, for 5 minutes.
In a small bowl, combine the water and cornstarch. Stir into the mushroom mixture. Cook and stir until the mixture is thickened and bubbly; cook and stir for 2 minutes more.
Add pork medallions to the mushroom sauce in the skillet; heat through. Transfer to a serving platter. Serve with rice or pasta. Garnish with parsley, if you like. Makes 4 servings.