Season chicken pieces with a pinch of salt and pepper. Heat oil in a large pot over medium-high. Add chicken and cook until golden on all sides, about 5 minutes. Transfer to a plate.
In the same pot, add onion and cook until softened, 3-4 minutes. Stir in garlic and taco seasoning, cooking for 1 minute until fragrant.
Pour in diced tomatoes with their juices, black beans, corn, chicken broth, and the seared chicken. Bring to a boil, then reduce heat to a gentle simmer.
Let the soup bubble gently for 20 minutes, or until chicken is cooked through, reaches an internal temperature of 165°F (74°C), and flavors meld. Stir in lime juice. Taste and adjust salt and pepper.
Ladle soup into bowls. Top with a handful of tortilla strips, shredded cheese, a dollop of sour cream, and fresh cilantro. Serve with extra lime wedges.