I used all lower-fat ingredients and it turned out perfect.
-1 pound ground beef
-6 flour tortillas (medium sized - I used Mission low-carb)
-1 medium onion, chopped
-2 cups salsa
-1 can black beans, drained and rinsed
-1 cup sour cream
-2 cups taco-flavored cheese
Preheat oven to 400 degrees. Brown ground beef with the onion, drain. Mix together with black beans, taco seasoning and salsa. Stir in sour cream. Spray the bottom of a 9x13 glass pan with cooking spray. Line with 3 tortillas. Top with half of the beef mixture and half the cheese. Repeat. Cover the pan with foil and bake for 35 minutes or until cheese is melted and bubbly.
Serve as is, or top with shredded lettuce, chopped tomatoes, chopped cilantro, hot sauce and extra sour cream.