Preheat the oven to 400°F.

Place the ground beef and diced onion in a large skillet over medium-high heat. Cook until the beef is completely browned and the onion is tender, breaking the meat into small pieces as it cooks.

Carefully drain away any excess grease from the skillet.

Reduce the heat to low and stir the taco seasoning into the beef mixture. Continue cooking for another 2–3 minutes so the seasoning can thoroughly coat the meat.

Divide the tortilla chips evenly between two large baking sheets. Spoon half of the refried beans over each tray, distributing them across the chips as evenly as possible.

Divide the seasoned beef mixture between the two trays. Sprinkle the shredded cheese evenly over the beef, beans, and tortilla chips.

Bake for 10–15 minutes, or until the cheese is completely melted and the nachos are heated through.

Remove the trays from the oven and immediately scatter the diced Roma tomatoes and chopped green onions over the top.

Serve the nachos while hot and crispy with your favorite optional toppings.