Preheat oven to 375°F. Mix cumin, chili powder, garlic powder, and salt in small bowl. Drizzle 1 tablespoon olive oil over chicken breasts and rub with some spice mix, reserving the rest. Bake chicken 20-25 minutes until internal temperature reaches 165°F. Shred with two forks. While chicken bakes, dice all vegetables.
Heat remaining olive oil in large soup pot (at least 6 quarts) over medium heat. Add onion, red bell pepper, green bell pepper, and garlic. Cook 3-4 minutes stirring frequently until softened. Add remaining spice mix and toast for 30 seconds.
Add shredded chicken and stir. Pour in Rotel tomatoes, chicken stock, tomato paste, hot water, and black beans. Bring to boil, then reduce heat and simmer uncovered for 45 minutes.
Mix cornmeal with 2-3 tablespoons of water in small cup to create slurry. Pour into soup and stir well. Simmer another 30 minutes until thickened. Taste and adjust seasoning. Remove from heat and let sit 15 minutes.
Right before serving, stir in tortilla strips. They will soften within 1-2 minutes. Ladle into bowls and top with desired toppings like sour cream, avocado, cheese, or cilantro.
Notes
Don’t skip the cornmeal as it thickens the soup and adds authentic corn flavor. Masa harina is the best substitute.
Bake chicken while chopping vegetables to save time. The soup gets better as it sits and flavors deepen.
For milder soup, use regular diced tomatoes instead of Rotel or reduce chili powder.
Freezes well for up to 2 months without toppings. Add fresh tortilla strips when reheating.
Use at least a 6-quart pot to accommodate all ingredients comfortably.