Start the aromatics.
Warm the olive oil in a large pot or Dutch oven over medium-high heat. Add the chopped onion and jalapeño, then cook until the onion softens. Stir in the garlic and cook briefly, just until fragrant.
Build the soup base.
Add the chicken breasts, fire-roasted corn, and green chiles. Season with Tajín, cumin, chile powder, salt, and pepper.
Simmer until the chicken is cooked.
Pour in the chicken stock, bring the pot to a boil, then lower the heat to a simmer. Cover and cook for about 25 minutes.
Shred the chicken.
Remove the chicken from the pot, shred it into bite-size pieces, and return it to the soup.
Make it creamy.
Stir in the sour cream, Monterey Jack, lime juice, and cilantro. Keep the heat low and let the soup warm through for a few minutes until the cheese melts and the broth turns creamy.
Finish and serve.
Ladle into bowls and top with queso fresco, extra cilantro, and lime wedges