Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Warm the olive oil in a large skillet over medium heat.
Add the onion and cook until softened, about 3–4 minutes. Stir in the garlic and cook 30 seconds.
Add the ground beef. Cook, breaking it up with a spatula, until browned and cooked through.
Drain excess fat if needed.
Sprinkle in the taco seasoning. Stir in the salsa, tomato sauce, black beans, and corn. Simmer 3–4 minutes, just until everything is hot and slightly thickened.
Taste and season with salt and pepper.
Spread half the crushed tortilla chips in the baking dish. Top with half the meat mixture and half the cheese. Repeat with the remaining chips, meat, and cheese.
Bake for 12–15 minutes, until the cheese is melted and bubbling.
While it bakes, toss the shredded romaine and cherry tomatoes with a squeeze of lime and a pinch of salt to brighten the flavor.
Remove the casserole from the oven and let it rest 5 minutes.
Top with the lettuce-tomato mix, olives, avocado, and cilantro.
Serve with sour cream or Greek yogurt and extra lime wedges. Add hot sauce if you like more heat.