Once it reaches a boil, stir in the pasta. Decrease heat and let it simmer, stirring often, until the pasta is cooked and the liquid has greatly reduced, about 10-14 minutes. After about 8 minutes, stir in the American cheese so that it melts through while the pasta finishes cooking. Once it's done, remove the pot from the heat and let it sit 5-10 minutes, then serve it up with your favorite chili toppings.