For the classic version, heat 1 tablespoon olive oil in a skillet over medium-high heat. Add the ground beef and cook for 6–8 minutes, breaking it into small pieces, until browned and no longer pink.

Drain excess fat if needed, then stir the taco seasoning and 1/2 cup water into the beef. Simmer for 2–3 minutes, stirring occasionally, until most of the liquid has evaporated and the meat is well coated.

For the vegetarian version, warm 1 tablespoon olive oil in a skillet. Add the black beans, pinto beans, and corn, sprinkle in the taco seasoning, add 1/3 cup water, and cook for 4–5 minutes.

Lightly mash some of the beans with the back of a spoon so the filling holds together while leaving plenty of whole beans for texture.

Place the chopped romaine in a large bowl or divide it among four plates. Arrange the beans, corn, tomatoes, red onion, avocado, cheese, and either warm taco filling over the lettuce.

Add the lightly crushed tortilla chips just before serving. Serve with salsa, sour cream, and lime wedges, or stir the salsa and sour cream together to make a quick dressing.