Stir oil and meat in 2 litre casserole until beef is coated. Cover and micro-wave on high (100%)) until meat is no longer pink, 4.5 to 5 Minutes.
Remove meat from casserole; reserve meat and juices.
Add mushrooms and onion to meat juices. Cover and microwave untilmushrooms are tender, 5 to 6 minutes.
Shake water and flour in tightly covered jar; stir into mushrooms. Sprinklewith dry mustard, salt and pepper. Microwave uncovered to boiling, 30seconds. Boil until thickened, 1 minute.
Stir in reserved meat, then sour cream. Microwave uncovered until hot,about 1 minute. Serve over hot cooked rice or hot cooked noodles.