Preheat the oven to 375°F and chop the onion and bell peppers.
In a large skillet, brown the ground beef, breaking it apart until no longer pink. Drain any grease.
Stir in taco seasoning, then add onions, peppers, black beans, and green chilies. Mix well.
Arrange the tortillas on a large sheet pan, overlapping slightly as directed.
Sprinkle half the cheese over the tortillas that are inside the sheet pan.
Spread the beef and veggie mixture evenly over the cheese.
Fold the remaining tortillas over the mixture, place a second sheet pan on top to hold them down, and bake for 20 minutes.
Remove the top pan, bake an additional 15 minutes. Cut into 8 squares (or 12 for smaller portions) and serve with sour cream, salsa, and green onions.