Heat vegetable oil in a large pot over medium heat. Once shimmering, add diced onion and cook for 4-5 minutes, stirring occasionally, until soft and translucent with slight golden edges.
Add minced garlic and diced bell pepper. Cook for 2-3 minutes until garlic is fragrant and peppers soften, turning a darker color.
Stir in cumin, chili powder, and oregano. Cook for 30 seconds, stirring constantly to release the spices’ aromas, being careful not to burn them.
Pour in enchilada sauce, chicken broth, and diced tomatoes. Stir well, scraping up any browned bits from the bottom. Bring to a gentle boil, then reduce to a simmer.
Add shredded chicken, black beans, and frozen corn. Simmer for 15-20 minutes, stirring occasionally, to allow the flavors to meld and the soup to thicken slightly.
Taste and adjust with salt and pepper as needed, depending on the saltiness of your enchilada sauce and broth.
Serve by ladling soup into bowls. Offer toppings like cheese (added while soup is hot), sour cream, avocado, tortilla strips, and a squeeze of fresh lime to finish.