Slice flat iron steak into thin bite sized pieces.
Brown onion and steak over moderate heat, add salt and black pepper to season.
Preheat oven to 350 degrees.
Finely chop two chipolte peppers (smoked jalapenos), add to pan with meat and onions and blend thoroughly.
In an oven safe 9x13 pan, spoon about 1/3 of enchilada sauce (19 oz. can) in bottom of pan.
Layer flour tortillas over enchilada sauce (it's perfectly ok to munch on only one tortilla at this time).
Spoon about half of the meat over the tortillas.
Repeat with another 1/3 of the enchilada sauce.
Repeat with another layer of the flour tortillas, remainder of meat and enchilada sauce.
Spoon about half of a 16 oz. jar of chunky salsa and sprinkle with cheddar and Monterrey Jack cheese.
Loosely cover with foil and place in a preheated 350 degree oven for thirty minutes.
Let the casserole stand for about 5 minutes before serving.
Now relax with a glass of wine and enjoy!