Preheat oven to 400 degrees. Coat a baking pan with cooking spray.
Add onions to a small, microwave-safe dish. Cook onions for 1 minute, to soften.
In a medium bowl, mix together cooked onions, chicken, salsa, cheese, corn, ranch or sour cream, and cumin.
Heat each tortilla in microwave for 10 seconds to soften. Heat 1 at a time. Once heated, place a little over ½ cup of chicken mixture in center of each tortilla and spread out a bit. Wrap like a burrito, folding opposite sides (ends) to close. Repeat for each by first heating tortilla in microwave, then adding filling and folding up.
Place each, seam-side down on a baking pan. Spray top of each with cooking spray. Bake in oven for 25 minutes or until golden brown. Remove each from baking pan using a spatula.
To Garnish: Top each chimichangas with ½ tablespoon skinny ranch dressing or sour cream, a little shredded lettuce, salsa, chopped tomatoes and 1 tablespoon cheese.