Place boneless pork loin chops between 2 sheets of waxed paper. Pound with meat mallet or rolling pin to 1/4-inch thickness. Season with salt and pepper, to taste.
Heat oil in large skillet over medium-high heat. Add pork; cook until browned on both sides and cooked through, about 6 minutes, turning once. Transfer to platter; keep warm.
Add onion to the same skillet used to cook boneless pork chops. Cook onion over medium-high heat, until golden and tender, about 2 to 3 minutes. Add the Marsala to the onion; bring to boiling, scraping up any browned bits from bottom of skillet. Remove skillet from the heat. Spoon sauce over boneless pork chops. Serve with hot rice, cooked following package directions.