Open a Slow Cooker Liner and line a 5- to 6 1/2-quart slow cooker bowl, ensuring the liner fits snugly along the bottom and sides and folds over the rim.
Place chicken breasts into the lined slow cooker.
Then layer sliced onions and bell peppers over the chicken.
In a bowl, mix together salsa, fajita seasoning, and cayenne pepper.
Pour the mixture evenly over the chicken and vegetables.
Cover the slow cooker with a lid on LOW for 6 to 7 hours or HIGH for 3 to 4 hours until the chicken is fully cooked and tender.
Carefully remove the lid, allowing steam to escape.
Use a wooden or plastic slotted spoon to gently stir the chicken and sauce.
Spoon approximately 1/2 cup of the chicken mixture onto a tortilla.
Add your favorite toppings, such as cheese, sour cream, guacamole, or cilantro, and fold the tortilla over the filling.
Once the slow cooker is completely cool, discard the liner and enjoy your flavorful chicken fajitas!