Fully cook the ground beef. Drain extra grease. Add water and taco seasoning then cook for 3 more minutes.
Cut avocado into small cubes.
Finely chop cilantro.
Meanwhile, preheat oven to 375 degrees F. Place empty taco shells on a cooking sheet and bake for 5 minutes.
Assemble each taco with meat mixture, tomatoes, avocado, cilantro and lettuce. Top it with sour cream and salsa. Sprinkle with shredded cheese. Serve immediately.