Mix all the ingredients in a large pot or slow cooker, except tortillas and cheese.
Bring it to a boil, then turn it down to simmer while you fix the tortilla strips. Or cook on high in the slow cooker for 4-5 hours.
For the tortilla strips, cut a stack of 10 tortillas in half. Then slice them into 1/4″ slices.
Fry in hot oil in a skillet and drain on paper towels.
Serve the soup with the tortilla strips and shredded cheese.