In a large skillet, over medium heat, add the chopped onion and minced garlic. Sauté until the onion is translucent, about 3-4 minutes.
Add the ground beef or turkey to the skillet. Cook until browned, breaking it apart as it cooks, about 6-8 minutes. Drain any excess fat.
Stir in the taco seasoning, black beans, corn, and diced tomatoes. Mix well and let the mixture simmer for 5 minutes. Season with salt and pepper to taste.
In a 9x13-inch baking dish, spread a thin layer of the meat mixture on the bottom. Place 3 corn tortillas over the mixture, overlapping slightly.
Sprinkle a third of the shredded cheese over the tortillas, followed by a layer of the meat mixture, and a handful of chopped cilantro. Repeat the layering process two more times, finishing with a layer of tortillas topped with cheese.
Cover the baking dish with foil and bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden.
Remove from the oven and let it cool for a few minutes before slicing.
Serve with a dollop of sour cream and garnish with additional cilantro and diced jalapeño if desired.
Notes
Feel free to add more vegetables or adjust the spice level with jalapeños.