Heat the olive oil in a large soup pot or Dutch oven over medium heat. Add the diced onion and minced jalapeño, then cook for 4 to 5 minutes, stirring occasionally, until the onion softens.

Add the minced garlic, cumin, and dried oregano. Stir continuously for 30 to 60 seconds, just until the garlic and spices smell fragrant.

Pour in the chicken broth and diced tomatoes. Add the chicken breasts, kosher salt, and black pepper, then bring the mixture to a gentle boil.

Reduce the heat and simmer the soup uncovered for approximately 18 to 22 minutes, or until the chicken reaches 165°F in the thickest part.

Transfer the cooked chicken to a plate and shred it with two forks. Return the shredded chicken to the soup and stir to distribute it through the broth.

Stir in the fresh lime juice and chopped cilantro. Taste the soup and adjust the salt, pepper, or lime juice as needed.

Ladle the soup into bowls and add the diced avocado immediately before serving. Finish with your favorite toppings, such as lime wedges, tortilla strips, sliced jalapeño, red onion, or Mexican crema.