Preheat oven to 400F. Cook mac n cheese as box says. While that''s cooking, brown meat; drain if needed. Add taco seasoning and water to meat; simmer 5 minutes or so.

Stir sour cream into mac n cheese. Spray 8 inch square baking dish with non stick cooking spray. Spoon half of the mixture into dish, top with the meat, half of the shredded cheese and then the rest of the mac n cheese mix. Cover with foil and bake for 15 minutes.

Remove from oven after 15 minutes and top with the salsa and rest of shredded cheese, and crushed tortilla chips(optional) and bake for another 5 minutes.