In a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain.
Stir in the salsa, beans, dressing, sour cream, corn (optional), taco seasoning and cumin.
Spoon a generous layer of meat mixture on bottom of 2 quart baking dish. Sprinkle with grated cheese.
Place a flour or corn tortilla on top of meat mixture. Layer with half of the meat mixture, and cheese. Repeat as many layers as you like.
The last & final layer should be a healthy dose of grated cheese.
Cover with foil that has been sprayed with pam or other and bake at 400 degrees for 25 minutes, or until hot & bubbly.
Let stand for 5 minutes before topping with lettuce, tomato and cilantro.