Start by slicing the boneless, skinless chicken breasts into thin strips. Then, chop your colorful bell peppers and onions into bite-sized pieces. Gather all the ingredients.

Place the sliced chicken, bell peppers, onion, and diced tomatoes in the slow cooker. Sprinkle the fajita seasoning generously over the top and stir to combine.

Cover the slow cooker and set it to cook on low for 6-8 hours or on high for 3-4 hours. Check for doneness around the 3-hour mark if using high.

Once cooked, remove the chicken and shred it using two forks. Mix back into the fajita mixture.

Serve warm with tortillas, lettuce wraps, or rice, and top with fresh garnishes.