Place chicken breasts in a heavy-bottomed pot or Dutch oven.
Whisk together chili powder, cumin, paprika, oregano, salt, and pepper in a small bowl.
Evenly coat the chicken breasts with the spice rub.
Add the diced onion, minced garlic, canned tomatoes (including liquid), and chicken broth to the pot.
Bring the mixture to a simmer over medium heat, then reduce heat to low and cover.
Cook for 25 to 30 minutes or until the chicken reaches an internal temperature of 165°F (74°C).
Transfer the chicken to a clean work surface and shred using two forks.
Return the shredded chicken to the pot with the cooking juices.
Stir in the lime juice and fresh cilantro before serving.