In a large pot, heat the oil over medium high heat just until shimmering--about 2 minutes.
Add the jalapeno, onion, garlic and chili powder. Reduce the heat to medium and cook until the onions start to soften. About 5 minutes.
Add the chicken stock and tomato paste and stir to combine. Taste before adding the salt in case your chicken stock is extra salty. Add half the salt, and all of the pepper, then allow to simmer 3 to 4 minutes, then taste the soup again. Add the rest of the salt if needed.
Add the chicken breasts to the simmering broth mixture, cover and cook until cooked through--about 15 minutes. Remove the chicken and allow to cool about 5 minutes, then cut the breasts in to 1-inch cubes, set aside.
Allow the broth to simmer uncovered 5 more minutes, then add the lime juice, cilantro, and chicken back to the pot. Ladle in to bowls and top with crushed tortilla chips, avocado slices, more fresh cilantro, diced tomatoes and a tablespoon of sour cream if desired.
Notes
Note 1: If your chicken stock is very salty just add half the salt as indicated in the recipe and adjust seasonings to taste.