Add the beef, onion, and taco seasoning to a skillet over medium heat. Brown the ground beef. Take off the heat and set aside.
Pour the black beans from the can, undrained, into a saucepan over medium heat. Sprinkle with salt, garlic powder, chili powder, and cumin. Stir occasionally until heated. Then, mash with a potato masher, leaving some beans whole. Take off the heat and set aside.
Add the diced tomatoes and Velveeta to another saucepan over medium heat. Stir until the cheese is completely melted and smooth.
Preheat the oven to 400°F. Line a large sheet pan with parchment paper.
Spoon a circular layer of cheese sauce (about the size of the can) in the middle of the sheet pan. Place the can directly over the circle of cheese sauce.
Layer the following in the can: tortilla chips, cheese sauce, meat, beans, shredded cheese, sour cream, BBQ sauce. Repeat these layers 3 more times.
Place the nachos in the oven for 10 minutes.
To make the pico de Gallo, combine the chopped jalapeño peppers, roma tomatoes, cilantro, and lime juice in a bowl.
Remove the nachos from the oven. Wearing oven mitts, gently lift the can up to reveal the tower of nachos. Drizzle with sour cream and BBQ sauce. Then, add the jalapeño slices, and a few spoonfuls of pico de Gallo and pickled onions on top.