Preheat oven to 400 °F.

In a skillet over medium heat, add the ground beef and diced onion. Cook, breaking up the meat, until beef is no longer pink. Drain any excess fat.

Reduce heat to low, add taco seasoning (and water if required by seasoning instructions). Simmer a few minutes until well combined.

On large baking sheets lined with parchment paper, spread the tortilla chips evenly from each bag.

Divide the refried beans by spoonfuls over the chips (you can warm the beans first for easier spreading).

Sprinkle half of the meat mixture over the two trays, then half of the shredded cheese. Then optionally repeat layers (chips → beans → meat → cheese) so toppings reach many chips.

Place trays in the oven and bake for ~10‑15 minutes, or until the cheese is melted and bubbly.

Remove from oven, then top with diced tomatoes and chopped green onions (and any additional fresh toppings).

Serve immediately with sour cream, guacamole, jalapeños or olives as desired.