2 teaspoons vegetable oil
3/4 cup onion, medium dice
1/4 cup carrot, peeled and medium dice
1/4 cup celery stalk, medium dice
1/4 cup red bell pepper, medium dice
1 medium garlic clove, minced
1/2 teaspoon chili powder
1 teaspoon ground coriander
1 teaspoon ground cumin
1/2 teaspoon dried oregano
1/2 teaspoon paprika
1/8 to 1/4 teaspoon cayenne pepper
4 cups low sodium chicken broth
1 cup water
1/2 cup canned crushed tomatoes
1 1/2 teaspoons kosher salt, plus more as needed
1/2 teaspoon freshly ground black pepper, more as needed
5 (6-inch) corn tortillas, cut into 1/2-inch pieces
2 cups, cooked chicken breast, cut in small cubes (I used rotisserie chicken)
1/2 cup 2% milk
Freshly ground black pepper
Crushed baked tortillas chips or tortilla strips
Thinly sliced green onion
Light sour cream
Heat the oil in a large saucepan or Dutch oven over medium heat until shimmering. Add the onion, carrot, celery, and bell pepper and season with salt and pepper. Cook, stirring occasionally, until the vegetables have softened, about 6 minutes.
Add the garlic, chili powder, coriander, cumin, oregano, paprika, and cayenne and cook, stirring occasionally, until fragrant, about 2 minutes. Add the broth, water, tomatoes, and measured salt and pepper, stir to combine, and bring to a boil.
Reduce the heat to low, add the tortillas, and stir to combine. Simmer, stirring occasionally, until the tortillas have disintegrated and the soup has thickened, about 1 hour.
When the thickened soup is finished simmering, add the chicken and milk and stir to combine. Simmer slowly until the flavors meld, about 15 minutes. Taste and season with salt and pepper as needed.
Serve the soup topped with your choice of garnishes.