In 12-inch skillet, heat oil over medium-high heat. Add patties; cook 4 minutes, turning once, until browned. Remove patties from skillet. Add mushrooms and onion; cook 6 minutes, stirring occasionally, until tender. Stir in gravy; heat just to boiling. Return patties to skillet; spoon gravy over patties. Reduce heat to low. Cover; simmer 8 to 10 minutes or until meat thermometer inserted in center of patties reads 160°F.