Position a rack in the center of your oven and preheat to 375°F (190°C). For easy cleanup, line a large, rimmed baking sheet with parchment paper.
In a large skillet over medium-high heat, cook the ground beef. Use a spoon or spatula to break it into small crumbles. Cook for about 5–7 minutes, until no pink remains. Drain off any excess grease to prevent the nachos from becoming soggy. Return the skillet to the heat, stir in the taco seasoning and water, and bring to a simmer. Let it cook for 4–5 minutes, stirring occasionally, until the sauce has thickened and coats the meat. Stir in the drained and rinsed black beans to warm them through.
The key to great nachos is strategic layering to avoid sogginess. First, spread the tortilla chips in an even layer on the prepared baking sheet. Sprinkle half of the shredded cheese directly over the chips. This creates a protective barrier against the moisture from the beef. Next, spoon the seasoned beef and bean mixture evenly over the cheese-covered chips. Top everything with the remaining shredded cheese and sprinkle with half of the sliced green onions.
Place the baking sheet in the preheated oven and bake for 8–10 minutes. You'll know they're ready when the cheese is completely melted, bubbly, and just starting to brown at the edges. Keep a close watch during the last few minutes to ensure they don't overbake.
Remove the nachos from the oven. Immediately sprinkle with the remaining green onions. Add your favorite fresh, cold toppings like diced tomatoes, jalapeños, or cilantro. To keep the nachos crisp, serve wetter toppings like salsa, sour cream, and guacamole on the side for dipping.