Place pork tenderloin in 16-oz shallow casserole [24-oz shallow casserole].
Sprinkle with salt and onion.
Cover tightly and microwave on medium (275 watts) 2 min [4 min]; rotate casserole 1/4 turn.
Microwave 2 min longer [4 min longer].
Mix remaining ingredients; spoon over pork.
Cover tightly and microwave, rotating casserole 1/4 turn every 3 min, until pork is done, 2 to 4 min [4 to 6 min].
Meat thermometer should register 170° when inserted in pork in several places.