Heat oil in a skillet or frying pan over medium-high heat. Add pork and onions; cook until evenly browned. Add mushrooms and saute for 5 minutes. Remove pork and vegetables and place on a side dish.
Return pan to heat, add butter and stir until melted. Add flour; stir constantly until a paste forms. Slowly add milk and stir until gravy thickens. Stir in tomato sauce, brown sugar, lemon juice and salt. Return pork mixture to pan, stir and simmer until meat is tender. Serve over noodles or rice.
