To prepare ahead of time, dice the onion and tomatoes and store in sealed container in the refrigerator. Add Doritos to large resealable bag. Break the Doritos into small pieces inside the bag. Store until ready to use.
Brown the ground beef. Add the seasoning packet. Stir. Do not add water as called for on the packet.
Add ground beef to a large bowl. Add Taco Sauce to ground beef. Stir.
Add scallions, tomatoes, and cheese to ground beef mixture. Stir.
Add lettuce to mixture and toss to blend all together.
Add the crumbled Doritos last and serve immediately after adding them.
Add more taco sauce over the top of salad when serving if desired.