In a blender, mix vinegar, vegetable oil, ketchup, sugar, one diced onion, Worcestershire sauce, salt and pepper.
When mixture is smooth, pour into a sealable container and refrigerate for at least one hour.
Brown ground beef, drain, and season with taco seasoning following directions on packet.
Refrigerate meat at least 20 minutes or until cool.
In a large serving bowl, layer lettuce, ground beef, tomatoes, one diced onion and cheddar cheese.
Just before serving, crush nacho-flavored tortilla chips in bag (hint: open the bag slightly at top to allow air to escape, or the bag will rupture).
Layer chips on top of salad and serve with chilled dressing on the side.