Preheat oven to 375°F (190°C) and grease a 9x13 baking dish.
In a skillet, sauté onion and garlic until soft.
Add cooked chicken and stir well.
Mix in taco seasoning and water; simmer 3–5 minutes.
Add salsa, black beans, and corn; cook 2–3 minutes.
Spread half of crushed tortilla chips in baking dish.
Add half of chicken mixture on top.
Sprinkle half of cheese over layer.
Repeat layers with remaining chips, chicken, and cheese.
Bake for 20–25 minutes until cheese is melted and bubbly.
Rest 5 minutes before serving.
Add toppings and serve warm.