Preheat your oven to 350 degrees F. Spray a 13 x 9 inch baking dish with cooking spray. Set aside.
Cook ground beef and onion in a large skillet over medium high heat until beef is browned, cooked through and no longer pink (about 8 minutes). Crumble beef while it is cooking with a wooden spoon. Drain off fat.
Return skillet with beef and onion to heat and reduce to medium low. Add taco seasoning, HALF of the enchilada sauce and green chiles. Stir to combine. Add HALF of the shredded cheese and stir until melted and combined. Remove from heat.
Wrap the stack of 8 tortillas in dampened paper towels and microwave for 1 minute.*
Evenly distribute beef mixture down the center of each tortilla. Wrap tortillas tightly and place seam-side down into prepared baking dish.
Pour the remaining half of the enchilada sauce over the tortillas, then sprinkle with the remaining shredded cheese.
Bake (uncovered) for 20 to 25 minutes, or until cheese is melted and sauce is bubbling around the edges of dish.
Top with desired toppings.