Preheat your oven to 375°F (190°C) and grease a 9x13 inch baking dish.
Brown the ground beef in a large skillet over medium heat, breaking it up as it cooks (about 7-8 minutes).
Add the diced onion and garlic to the meat, cooking until the onion becomes translucent (about 3-4 minutes).
Stir in the taco seasoning and diced tomatoes. Simmer for 5 minutes.
Mix in the black beans and heat through.
Layer half of the crushed tortilla chips in the bottom of the prepared baking dish.
Spread the meat mixture evenly over the chips.
Sprinkle with half the cheese.
Add remaining tortilla chips on top and finish with the remaining cheese.
Bake for 20-25 minutes, or until the cheese is melted and bubbly.
Let stand for 5 minutes before serving.
Top with shredded lettuce, tomatoes, and sour cream.