Heat oven to 350°F. In 10-inch skillet, cook beef over medium-high heat 5 to 7 minutes, stirring occasionally, until thoroughly cooked; drain. Stir in beans, tomato sauce and taco seasoning mix. Reduce heat to medium; heat to boiling, stirring occasionally.
In ungreased 1 1/2- to 2-quart casserole, place tortilla chips. Top evenly with beef mixture. Sprinkle with onions, tomato and cheese.
Bake uncovered 20 to 30 minutes or until hot and bubbly. Arrange additional tortilla chips around edge of casserole.