Heat a large skillet over medium-high heat. Add the lean ground beef and diced yellow onion, then cook for 6–8 minutes while breaking the meat into small crumbles, until browned and no longer pink; drain excess fat if necessary.

Stir the taco seasoning and 2/3 cup water into the cooked beef. Simmer for 2–3 minutes, stirring occasionally, until the liquid is mostly absorbed, then remove the skillet from the heat and let the beef cool slightly.

Place the chopped romaine or iceberg lettuce in a large serving bowl, or divide it among four bowls. Make sure the lettuce is well drained so the salad stays crisp.

Arrange or add the beans, corn, chopped tomatoes, sliced red onion, shredded cheese, diced avocado, and slightly cooled taco beef over the lettuce. Keep the ingredients in colorful sections for a composed presentation, or toss gently for an evenly mixed salad.

Scatter the lightly crushed tortilla chips over the top immediately before serving. Offer salsa and sour cream on the side, or toss the salad with Catalina or French dressing right before eating.