For Serving (all optional, but I'd say sour cream is a must):
Additional shredded Cheddar and Monterrey Jack Cheese
Chopped green onions
Tortilla Chips or strips
Place chicken in a slow cooker. Pour chicken broth, tomato sauce, salsa and Zesty Italian Dressing over chicken. Sprinkle in chili powder, cumin, onion powder and garlic powder. Cover with lid and cook on low heat for 6 hours.
Once cooked, remove chicken from slow cooker and set aside. Prepare a roux in a saucepan by heating olive oil over medium heat then stirring in Masa Harina (mixture will be thick), slowly pour in milk. Cook, stirring constantly, until mixture is very thick and it reaches a gentle boil (it should be like the consistency of a porridge). Pour mixture into slow cooker and whisk until smooth.
Add in corn, Black Beans, Pinto Beans, Cheddar Cheese and Monterrey Jack Cheese. Shred chicken and stir into soup. Season soup with salt and pepper to taste (I didn't add any salt at all I didn't think it needed it just pepper). Allow to cook about 10 minutes until all ingredients are heated through. Serve warm garnished with additional shredded cheese, diced avocados, sour cream, cilantro, green onions and tortilla chips.