Dice the onions, finely dice the cilantro (optional), and set aside.
Grate the cheese and set aside.
Heat 2 tablespoons of avocado oil in a large pot over medium heat. Add the cubed or shredded chicken, season with salt and pepper, and cook for 5-7 minutes until golden brown and cooked through. Remove the chicken from the pot and set it aside.
In the same pot, add the diced onion and minced garlic. Sauté for 3-4 minutes until softened and fragrant.
Stir in 1 teaspoon ground cumin, 1 teaspoon chili powder, and 1 teaspoon ground coriander. Cook for 1 minute, then add the diced tomatoes and let them cook for 3-4 minutes until they break down slightly and blend with the spices.
Pour in the enchilada sauce and stir to combine. Add the chicken broth and return the cooked chicken to the pot.
Stir in the black beans (drained and rinsed) and corn. Bring the soup to a boil, then reduce the heat and let it simmer for 15-20 minutes to meld the flavors.
Remove the soup from heat and stir in the sour cream until fully combined and smooth. For extra richness, you can stir in heavy cream at this point.
Stir in the shredded cheese until melted and the soup is creamy.
Taste and adjust seasoning with salt and pepper if needed. Add a splash of lime juice if you like.
Ladle the soup into bowls and garnish with tortilla strips, avocado, cilantro, extra cheese, or lime wedges if desired.