Heat the olive oil in a large pot over medium heat.
Add the chopped red onion and minced garlic; cook, stirring, until soft, about 3 minutes.
Add the chicken broth, fire-roasted diced tomatoes, fresh cilantro, black beans, corn, ground cumin, dried oregano, and whole chicken breasts (if using) to the pot.
Bring the soup to a boil, then reduce heat to a simmer.
Cook the soup on low simmer for 1 hour.
Remove the chicken breasts from the pot and shred with two forks; return shredded chicken to the pot.
If using rotisserie chicken, add it now.
Stir in 2 cups of Cabot Cheese and cook for an additional 10 minutes.
Season with salt and pepper to taste.
Ladle the soup evenly into bowls.
Serve with your choice of toppings such as cheese, red onion, cilantro, sour cream, salsa, avocado, and tortilla chips.
Enjoy your Healthy Chicken Tortilla Soup!