Preheat oven to 350°. Wash the tomatoes, dry, and chop.
Heat the oil in a frying pan. Add the onion and cook on medium-low heat until tender. Add the ground beef. Stir in the taco seasoning. Cook until the ground beef is browned. Drain off fat from pan.
Spread out approximately half of the tortilla chips in the bottom of a 9″ × 13″ × 2″ glass baking dish. Spoon the cooked ground beef over the chips. Sprinkle 1 cup of the shredded cheese over the ground beef. Cover with the remaining chips (there will probably be a few chips left over), and 1 cup of the cheese. Sprinkle the tomatoes and olives (if using) on top. Sprinkle the remaining cheese on top.
Bake the nachos for 5 minutes or until the cheese is melted. Serve hot.
To spice up this dish, mix canned jalapeño peppers in with the shredded cheese before cooking. Serve with traditional nacho accompaniments, such as sour cream.