Slice the red, yellow, and green bell peppers into 1/2-inch thick strips, halve the yellow onion and slice into 1/2-inch wedges, and mince the garlic cloves. This mise en place preparation ensures you're ready to layer ingredients efficiently into the crockpot without delays once cooking begins.
Add half of the chunky salsa to the bottom of your crockpot to prevent sticking and create a flavorful base. Layer in half of the sliced peppers and onions, then scatter the minced garlic over top. This layering technique helps distribute flavors evenly throughout the cooking process and ensures the vegetables don't all settle to the bottom.
Place the chicken breasts directly on top of the vegetable layer. Sprinkle the fajita seasoning packet and ground cumin evenly over the chicken, making sure it's well-coated. I find pre-seasoning the chicken this way allows the spices to penetrate the meat as it cooks slowly, building deeper flavor throughout.
Top the seasoned chicken with the remaining half of the sliced peppers and onions, then pour the remaining salsa and fresh lime juice over everything. This top layer of vegetables and liquid helps keep the chicken moist and creates steam for even cooking. The lime juice will brighten the flavors as everything cooks together.
Cover the crockpot and cook on low for 6-8 hours or on high for 3-4 hours, until the chicken reaches an internal temperature of 165°F. The long, gentle cooking allows the chicken to become tender and absorb all the spices and salsa flavors while the vegetables soften perfectly.
Remove the chicken breasts from the crockpot and shred them using two forks, then return the shredded chicken to the pot and stir everything together. Taste the mixture and season with salt and pepper as needed. I like to add the cilantro right at the end so it stays fresh and bright rather than wilting during the long cook time—stir it in just before serving.
Ladle the shredded chicken and vegetable mixture into warm flour or corn tortillas and serve with your favorite toppings such as sour cream, guacamole, shredded cheese, or additional cilantro.