To make the sauce, melt the butter over medium heat in a small saucepan. Add the cornstarch and salt and stir until well combined. Add the milk and stir constantly until boiling. Continue to stir and boil for one minute. Reduce heat to low and add the cheese, stirring until cheese is completely melted. Keep on low heat until ready to add to the nachos.
Heat the chicken, black beans and jalapenos over medium heat in a saucepan until heated through.
Arrange the tortilla chips on a large jelly roll pan. Pour the cheese sauce over the chips, and then add the chicken/bean mixture. Sprinkle the remaining ingredients on top (tomatoes, olives, guacamole, sour cream, etc) and then serve immediately.
If you want the chips to be a little more crispy and you want the tomatoes, olives, etc. heated too, you can place the whole tray in the oven at 400° for about about 8-10 minutes (before guacamole or sour cream). This step is totally optional as the cheese, chicken and beans will be heated up and warmed already, even without the oven!