Heat oven to 350°F. Heat oil in large skillet over medium-high heat until hot. Add onion; sprinkle with sugar. Cook 12 to 15 minutes or until onion is soft and golden brown, stirring frequently.
Spray 13x9-inch pan with nonstick cooking spray. Place pork tenderloin in sprayed pan. Sprinkle with salt and pepper. Top with onion mixture.
Bake at 350°F. for 40 to 50 minutes or until no longer pink in center and thermometer inserted in center registers 160°F.