Step 1

Preheat oven to 450 degrees F. Coat 2 rimmed baking sheets with cooking spray.

Step 2

Place chicken on one of the prepared pans and sprinkle with 1/4 teaspoon salt and pepper. Spread tomatillos, onions, jalapeños and garlic on the other pan. Transfer both pans to the oven. Roast the chicken, flipping once, until an instant-read thermometer inserted in the thickest part registers 165 degrees F, 15 to 25 minutes. Roast the vegetables, stirring occasionally, until tender and browned, about 25 minutes. Reduce oven temperature to 375 degrees.

Step 3

Shred the chicken. Transfer the vegetables to a blender. Add cilantro and the remaining 3/4 teaspoon salt; blend until smooth, about 30 seconds.

Step 4

Spread 1/2 cup sauce in a 9-by-13-inch baking dish. Pour 2 1/2 cups sauce into a pie pan. (Refrigerate or freeze the remaining sauce for another use; see Tip.) Dip 1 tortilla in the sauce in the pie pan, coating both sides. Top the tortilla with 1/4 cup chicken and 1 tablespoon cheese. Roll up and place, seam-side down, in the baking dish. Repeat with the remaining tortillas, chicken and 7 tablespoons cheese. Top the enchiladas with the sauce remaining in the pie pan and the remaining 1/2 cup cheese.

Step 5

Bake until the sauce is bubbling and the cheese is melted, 20 to 25 minutes. Serve with desired toppings.