Add ground chuck and onion to large skillet over medium-high heat, cook ground beef until no longer pink. Stir in salsa, taco seasoning, then reduce heat, and let simmer for 20 minutes, or until liquid is absorbed. Stir in beans, and heat through.
Spray a 9x13 baking dish with cooking spray or coat down with olive oil.
Spread crushed tortilla chips in dish, and then spoon beef mixture over chips.
Spread sour cream over beef; sprinkle corn, mushrooms, chilis, olives, and fresh tomato over the sour cream.
Top with Cheddar cheese.
Bake in preheated oven for 30 minutes, or until hot and bubbly.