Heat oil in a large skillet. Brown the sirloin tips; sprinkle with salt and pepper. Add mushrooms to meat; cover and cook for 10 minutes. Sprinkle in the green onions. Combine sour cream and prepared brown gravy; stir until smooth. Add sauce to meat mixture; simmer for 5 to 10 minutes, until heated through. Serve beef stroganoff over hot cooked noodles or rice.
Beef stroganoff recipe serves 4 to 6.