In a large pot, heat the oil over medium heat. Add the onion and garlic and cook, stirring until soft, about 3 minutes. Add to the pot the remaining soup ingredients (including whole chicken breasts if using). Bring to a boil, then turn down to a simmer. Cook the soup on simmer for 1 hour.
Remove the chicken breasts from the pot and shred, and put back into the pot. Or at this time add rotisserie chicken if you are using. Add 2 cups of cheese. Cook for additional 10 minutes. Salt and pepper to taste!
To serve, ladle into bowls, dividing evenly. Serve with toppings and enjoy!