Cheesy Beef Corn Chip Skillet

1 lb ground beef
1 small onion, chopped
3/4 cup water
1 pkg taco seasoning mix
2 cups corn chips
1/4 lb velvetta, cut into 1/2 inch cubes
2 cups shredded lettuce
2 tomatoes, chopped

Brown meat with onions in large skillet; drain. Add water and seasoning mix; cook as directed on package. Cover meat mixture with chips and velvetta; cover. Cook on low heat 5 min. or until Velvetta is melted. Top with lettuce and tomatoes.