Heat the olive oil in a large pot or Dutch oven over medium heat. Once hot, add the onion and season with pepper. Cook onion for 5-6 minutes or until translucent and softened.
Add the tomatillos, carrots, and poblano peppers; continue cooking another 6-8 minutes or until the tomatillos soften.
Pour in the enchilada sauce and chicken broth; bring the soup to a boil. Add the chicken and corn, cover, and reduce the heat to low. Simmer 20 minutes or until the chicken is cooked through. Remove the chicken to a cutting board and shred the chicken with two forks; return to pot.
Remove from the heat and stir in the cilantro. Top with avocado, cheese, and/or tortilla strips, if desired.