Heat the oil in a large pot or Dutch oven over medium-high heat. Add the onion and jalapeño, cooking until the onions soften, about 3 to 4 minutes. Stir in the garlic and cook for another 30 seconds until fragrant.
Add the chicken, fire-roasted corn, and green chiles to the pot. Season generously with Tajín, cumin, chili powder, salt, and pepper to create a flavorful base.
Pour in the chicken stock and bring it to a boil over high heat. Once boiling, reduce the heat to a simmer, cover, and let the soup cook for 25 minutes so all flavors meld beautifully.
Remove the chicken from the pot once cooked thoroughly and shred it into bite-sized pieces using two forks or your hands before returning it back into the pot.
Stir in sour cream, Monterey Jack cheese, lime juice, and cilantro into the pot while simmering on low for another 3 minutes until everything is heated through and combined well.
Dish out your delicious soup into bowls topped with crumbled queso fresco, lime wedges, and additional chopped cilantro for an eye-catching presentation that enhances flavor too!