Heat oven to 350 F. Line two large rimmed baking sheets with foil. Arrange half of the chips on pans and top with some cheeses, beans, onion, and jalapeño. Repeat layers for two to three layers total. (These can be assembled up to one hour before baking.)
Working with one sheet at a time, bake until cheese is melted, 10 to 15 minutes. Sprinkle with cilantro, scallions and olives if desired and serve with desired toppings. Heat a second pan as the first for fresh, hot nachos.