Start by rinsing the boneless skinless chicken breasts under cold water and patting them dry with paper towels.
Place the chicken breasts in the bottom of the slow cooker. In a separate bowl, mix together the Italian dressing mix, lemon juice, chicken stock, and crushed garlic cloves. Pour this mixture over the chicken.
Cut the butter into small pieces and scatter them on top of the chicken. Then, add the drained capers, ensuring they are evenly distributed throughout the mixture.
Cover the slow cooker with its lid and set it to cook on low for 6 to 8 hours, or on high for 3 to 4 hours.
Once the cooking time is up, carefully remove the chicken breasts from the slow cooker. Use two forks to shred the chicken, and then return it to the slow cooker, mixing it with the sauce. Serve warm over rice, pasta, or with a side of roasted vegetables.