Slice your bell peppers and onion, then place them at the bottom of your slow cooker. Lay the chicken breasts on top of the vegetables, sprinkle with fajita seasoning, garlic, and salt and pepper.
Pour the chicken broth and lime juice over the chicken and veggies, drizzle with olive oil, and give everything a light mix. Cover the slow cooker and cook on low for 6-7 hours, or on high for 3-4 hours.
Once the chicken is cooked through, remove it from the slow cooker and shred it with two forks. Stir the shredded chicken back into the slow cooker to soak up the juices. Serve with warm tortillas and your favorite toppings!