Preheat oven to 375°F. Cook ground beef, onion and bell pepper in large skillet on medium heat 5 minutes or until cooked through, stirring frequently. Drain, if needed. Stir in Seasoning Mix and water. Simmer 5 minutes, stirring occasionally.
Arrange tortilla chips in single layer on 2 lightly greased foil-lined shallow baking pans, overlapping chips if needed to cover bottom completely. Top each pan of chips with 1/2 each of the meat mixture and the cheese.
Bake 5 minutes or until cheese is melted. Serve immediately with assorted toppings, if desired.