Preheat oven to 350. Lightly grease 2 9x13 glass baking dishes with non-stick cooking spray.
In a large mixing bowl, mix together the shredded chicken, sour cream, spinach, 1 cup of the pepper jack cheese, minced onion and garlic, cumin and some salt and pepper.
Spoon the mixture into each of the tortillas. Roll, and place the tortillas seam side down in the baking dish. (I can generally fit 8 to 10 enchiladas in a pan, depending on how full they are and how tight they are rolled.) Fill both pans.
Then pour 1 can of the green enchilada sauce over the top of 1 pan, and repeat with the other can. Sprinkle the remaining 3 cups of pepper jack cheese over the 2 pans.
Bake in the preheated oven for 30 minutes, or until cheese is melted and begins to golden, and sauce is bubbling.