If using traditional lasagna noodles, cook them in well-salted water according to package directions. Drain and set aside.
In a large skillet, heat the oil over medium heat. Add the onions and cook for 5-7 minutes until softened. Stir in the green chiles.
Add the chicken and 1¼ cups of enchilada sauce. Stir to combine. Heat for 1-2 minutes.
Coat a 9x9 baking dish with cooking spray. Place 3-4 lasagna noodles to cover the bottom of the dish. Spoon half of the chicken mixture over the top. Sprinkle ⅓ of the cheese over the chicken.
Layer 3-4 more lasagna noodles on top of the cheese. Top with the remaining chicken mixture and another ⅓ of the cheese. Top with 3-4 more noodles. Cover with the remaining enchilada sauce and the rest of the cheese.
Bake at 375 degrees for 30-40 minutes until golden and bubbly.
Assemble ahead of time and bake when ready. This helps with those busy nights when you need dinner in a flash. If refrigerated, allow 10-15 minutes of extra baking time unless the casserole is brought to room temperature first.
To freeze the unbaked casserole, cover it with foil and wrap it tightly with plastic wrap. Then, thaw before baking.