Brown ground beef with taco seasoning until cooked.
Drain excess fat and let it cool slightly.
In a bowl, mash ripe avocados and mix with lime juice.
Add chopped tomatoes, black beans, and corn to the beef.
Toss with the avocado-lime dressing.
Season with salt and freshly ground black pepper.
Serve over a bed of shredded lettuce.
Top with shredded cheddar cheese for extra flavor.