Cook beef and onion in large skillet until beef is browned, stirring until it crumbles. Drain.
Stir tomato sauce and next 7 ingredients into meat mixture; bring to a boil. Reduce heat to medium, and cook, uncovered 5 minutes, stirring occasionally.
Place half of the tortillas in bottom of a greased 9X13 baking dish. Spoon half of beef mixture over tortillas. Sprinkle with 1 cup of cheese. Repeat layers with remaining tortillas and beef mixture. Bake 375 degrees for 10 minutes. Sprinkle with remaining cheese and bake 5 more minutes until cheese melts. Casserole should be hot and bubbly. Garnish with green chile peppers if desired.