Peel the onions, and trim off both ends.
Slice onions thinly, roughly about ⅛-inch thick.
Pat dry with a paper towel.
Place onions in a plate or shallow bowl, and spray with cooking oil.
Toss to coat the onions.
Spread them into a thin layer, and place in the microwave.
Microwave for about 5 minutes, tossing them with a fork every 2 minutes, or until the onions are brown and crispy.