Mix margarine and browning sauce.
Brush half of the margarine mixture over both sides of beef tenderloin.
Place beef on rack in 11 x 7 x 1 1/2" dish.
Cover with waxed paper and microwave on medium (275 watts) 3 min [5 min]; rotate dish 1/2 turn.
Place mushrooms on rack around beef; brush with remaining margarine mixture and sprinkle with basil.
Cover with waxed paper and microwave until meat thermometer inserted horizontally in beef registers 135°, 2 to 3 min [1 to 3 min].
Spoon beef juices over beef and, if desired, sprinkle with salt and pepper.
Sprinkle mushrooms with grated Parmesan cheese if desired.