Prep the veg. Slice the bell peppers and onion into thin strips.
Mince the garlic if using fresh.
Mix the seasoning. In a small bowl, combine chili powder, cumin, smoked paprika, oregano, salt, pepper, and cayenne (if using). Zest the lime and set aside.
Layer the slow cooker. Drizzle olive oil in the bottom. Add half the peppers and onions, then place the chicken on top.
Sprinkle the seasoning mix evenly over the chicken. Add remaining peppers and onions.
Add liquids. Pour in the chicken broth and the can of diced tomatoes with their juices. Scatter in the minced garlic.
Do not stir.
Cook low and slow. Cover and cook on Low for 4–5 hours or High for 2–3 hours, until the chicken is tender and reaches 165°F internally.
Shred and finish. Remove the chicken to a cutting board and shred with two forks. Return it to the slow cooker, add the lime zest and juice, and stir. Taste and adjust salt, pepper, or lime as needed.
Build your bowls. Spoon rice or your chosen base into bowls.
Top with the fajita chicken and veggies. Add cilantro, avocado, cheese, and your favorite extras.
Serve. Enjoy warm. The mixture will be slightly saucy—perfect for spooning over rice.