In large skillet, cook onion and sugar in oil over medium-low heat until onion is tender and golden brown, about 30 minutes, stirring occasionally.
Place pork in 13 x 9 x 2-inch baking dish coated with nonstick cooking spray. Sprinkle with salt and pepper. Top with onion mixture. Bake, uncovered, at 350° 40 to 45 minutes or until meat thermometer reads 160°. Let stand 5 minutes before slicing.