Preheat the Oven: Preheat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Cook the Ground Beef: Heat a large skillet over medium heat. Add the ground beef and diced onion. Cook until the beef is browned and the onion is tender.
Add Garlic and Seasoning: Add the minced garlic and taco seasoning. Stir well and cook for another minute until fragrant.
Add Beans, Corn, and Salsa: Stir in the drained black beans, corn, and salsa. Cook for a few minutes until the mixture is hot and well combined.
Start the Layers: Spread a thin layer of the beef mixture across the bottom of the prepared baking dish. Place a layer of flour tortillas over the filling.
Add More Filling and Cheese: Spread another layer of the beef mixture over the tortillas. Add salsa and sprinkle generously with shredded Mexican cheese.
Continue Layering: Repeat the tortillas, beef mixture, salsa, and cheese until all the ingredients have been used. Finish with a generous layer of cheese on top.
Bake: Cover the dish with aluminum foil and bake for about 25 minutes.
Brown the Cheese: Remove the foil and continue baking for another 8–10 minutes, or until the cheese is melted, bubbly, and lightly golden.
Rest and Serve: Remove the lasagna from the oven and let it rest for 5–10 minutes. Garnish with fresh cilantro, sour cream, and sliced jalapeños if desired. Slice and serve warm.