In a Dutch oven or large soup pot, melt the butter or ghee over medium-high heat, adding avocado oil if preferred.
Add the diced onion, sliced celery, thinly cut carrot, chopped garlic, and diced bell pepper, and sauté until softened, approximately 5–6 minutes.
Incorporate the cumin, chili powder, and oregano into the vegetables. Stir in the fire-roasted tomatoes, tomato paste, and chicken broth. Season with salt and pepper as needed, bring the mixture to a boil, then lower the heat and allow to simmer for 10–15 minutes until the vegetables are thoroughly tender.
Remove the pot from heat and use an immersion blender to puree the mixture until it achieves a smooth and creamy texture. Return the soup to the heat.
Mix in the black beans, red kidney beans, corn, and shredded chicken. Allow the soup to come to a gentle boil, cooking just enough to warm the added ingredients through.
Ladle into serving bowls and garnish each portion with a sprinkle of the shredded cheese blend or toppings of your choice. Serve immediately.