Cook ground beef in a skillet over medium heat until browned. Drain fat.
Stir in taco seasoning and water. Simmer over medium-low heat for 3 to 5 minutes. Let cool slightly.
In a large bowl, combine lettuce, cheese, tomatoes, and red onion.
Add beef and dressing. Toss to coat.
Fold in crushed Doritos just before serving. Garnish with green onions.
Notes
Add the Doritos just before serving so they stay crunchy.
Let the taco meat cool slightly before adding it to the salad so it does not wilt the lettuce.
Start with less dressing and add more as needed. Depending on the size of your lettuce, you may not need the full cup.
For make-ahead prep, cook the taco meat and chop the vegetables in advance. Store everything separately and toss together right before serving.
Leftovers can be stored in the refrigerator for up to 2 days, but the lettuce and Doritos will soften as they sit.
Substitutions: Ground turkey, ground chicken, or plant-based ground can be used instead of ground beef. Catalina dressing can be used in place of French dressing. Cheddar can be swapped with Tex-Mex, Monterey Jack, Colby Jack, or a taco cheese blend. Cool Ranch or Spicy Nacho Doritos can also be used for a different flavor.