1. Trim fat from pork. Cut pork into 1-inch-thick slices. Place slices between two sheets of heavy-duty plastic wrap, and flatten to 1/2-inch thickness, using a meat mallet or rolling pin. Sprinkle with thyme, salt, and pepper.
2. Place a large nonstick skillet coated with cooking spray over medium heat until hot. Add pork; cook 3 minutes on each side or until browned. Remove from skillet, and keep warm.
3. Heat oil in skillet over medium heat; add onion. Cook 8 to 10 minutes or until onion is tender, stirring often. Add vinegar and honey; cook, stirring constantly, 1 minute or until onion is glazed. Spoon onion over pork.