Cook the ground beef, and saute onions until the meat is brown, about 15 minutes. Drain the fat. Combine with chili powder, salt and pepper. Reserve 1 cup cheese in a 1-quart freezer bag to use when serving. Spoon enough meat mixture and cheese on each tortilla to cover a third of it. Roll tortilla beginning at the filled edge. Place seam side down in a 13x9x2-inch baking dish treated with nonstick spray. When tortillas are completed, combine soup, sour cream, and green chilies to make a sauce; pour over tortillas. Cover dish with foil and freeze with bag of cheese taped to it.
To prepare for serving, thaw enchiladas and cheese. Bake uncovered in a preheated 375ºF oven for 20 to 25 minutes. The last 10 minutes sprinkle the remaining cheese on top.