Make the Pico de Gallo by mixing together ½ of the chopped onion, 3 Roma tomatoes, jalapeño, cilantro, lime juice, and salt. Set aside.
Add the beef and other ½ of the chopped onion to a non-stick skillet over medium-high heat. Cook until no longer pink and the onions are translucent. Drain off the fat, and mix in the water and taco seasoning. Bring to a simmer, cover, and turn down to low. Simmer for 8-10 minutes until tender.
Stir in the black beans (add another ¼ cup of water if too thick) and simmer another 4-5 minutes.
Meanwhile, line a large rimmed baking sheet with a layer of chips.
Spoon half the meat/bean mixture over the chips followed by half the cheese. Add a second layer of chips and repeat with meat mixture and cheese. Place in the oven for 3-5 minutes until cheese is melted.
Top with pico de gallo, avocados, extra cilantro, and sour cream. Serve immediately.