Mix together the onion, tomatoes, parsley, olive oil, lime juice, salt and pepper in a bowl.
Spread tortilla chips in a single layer onto a baking sheet, and spoon about 1 teaspoon of the tomato salsa onto each chip. Spread 1 cup of Cheddar cheese over the nachos, top the chips with another teaspoon or so of salsa, and top with the remaining 1 cup of cheese.
Bake the nachos in the preheated oven until the cheese is bubbling, about 5 minutes. Serve hot with sour cream, guacamole, and any remaining salsa on the side for dipping the chips.