Preheat your oven to 350°F (175°C) and lightly grease a 9x13 inch baking dish.

In a large skillet over medium-high heat, cook the ground beef and onion until the meat is browned and onions are translucent, about 5-7 minutes. Drain any excess fat.

Add minced garlic to the skillet and cook for 30 seconds until fragrant.

Stir in the taco seasoning, black beans, corn, and diced tomatoes with green chilies. Reduce heat to medium-low and simmer for 5 minutes, allowing the flavors to blend.

Layer half of the crushed tortilla chips on the bottom of the prepared baking dish.

Spread the meat mixture evenly over the tortilla chips.

Dollop the sour cream over the meat mixture and gently spread it with the back of a spoon.

Sprinkle 1 cup of the shredded cheese over the sour cream layer.

Top with remaining crushed tortilla chips and the rest of the cheese. Sprinkle black olives on top if using.

Cover the dish with aluminum foil and bake for 30 minutes.

Remove the foil and bake for an additional 10-15 minutes until the cheese is bubbly and golden.

Let the casserole rest for 5 minutes before serving. Garnish with sliced green onions and fresh cilantro.