Heat olive oil in a large skillet over medium-high heat. When hot, add chopped onion then cook, stirring occasionally, until softened. Add ground beef, then season with Kosher salt, and taco seasoning. Cook until browned. Stir well.
In a large bowl, combine chopped Romaine lettuce, ground beef, thinly sliced green onions, black beans, corn, tomatoes, avocado, and cotija or Cheddar cheese. You can either crumble tortilla chips on top or save them for serving. Drizzle with as much of the dressing as you like, then toss well to thoroughly mix.
Serve immediately with tortilla chips, fresh cilantro, and lime wedges!