Pat the chicken breasts dry and place them in the bottom of a large slow cooker.
In a small bowl, whisk together the garlic powder, chili powder, kosher salt, onion powder, ground cumin, black pepper, chipotle powder, and smoked paprika. Evenly sprinkle this spice mixture over all sides of the chicken breasts.
Pour the entire can of undrained fire-roasted diced tomatoes with green chilies over the seasoned chicken. Add the bay leaf to the pot.
Cover the slow cooker with its lid. Cook on the LOW setting for 5-6 hours, or on the HIGH setting for 3-4 hours, until the chicken is fully cooked and shreds easily with a fork.
Approximately 30-45 minutes before the total cooking time is complete, add the sliced bell peppers and onion to the slow cooker, distributing them over and around the chicken. Re-cover and continue cooking until the vegetables have softened to your liking (30 minutes for slightly crisp, 45 minutes for softer).
Once cooking is finished, carefully remove the chicken breasts from the slow cooker and place them on a clean cutting board or in a large bowl. Discard the bay leaf from the slow cooker.
Using two forks, shred the cooked chicken to your desired consistency.
Return the shredded chicken to the slow cooker, along with any accumulated juices and the cooked vegetables. Stir in the fresh lime juice until everything is well combined.
Serve the chicken fajita shreds warm. Offer with low-carb tortillas or lettuce wraps, and your favorite toppings such as sour cream, guacamole, salsa, and shredded cheese.