Heat oven to 350°F.
In 10-inch skillet, heat oil over medium heat. Cook onion in oil about 3 minutes or until onion begins to soften. Add green chiles and chicken, stirring well. Stir in 1/2 cup of the cooking sauce, stirring well to combine. Remove from heat; stir in 1/2 cup of the cheese.
Spray 11x7-inch (2-quart) glass baking dish with cooking spray. Using remaining cooking sauce, brush both sides of each tortilla. Spoon about 1/3 cup filling in each tortilla. Fold tortillas around filling, and place seam side down in pan. Sprinkle with remaining 1/2 cup cheese.
Bake 20 to 25 minutes or until enchiladas are heated through. Top with sour cream and sliced avocado.