Mix the spices: Mix the garlic and onion powder, dried parsley and dill weed, and salt in a small bowl.
Season the chicken: Place the chicken breasts in the slow cooker and sprinkle the spice mix evenly over the chicken.
Mix and pour the liquids: In a small bowl, whisk together the chicken broth, pepperoncini liquid, cornstarch, soy sauce, and Worcestershire sauce until the cornstarch is fully dissolved. Pour the mixture evenly over the seasoned chicken, then top with the butter pieces and pepperoncini peppers.
Cook: Cover and cook on low for 6–8 hours or high for 3–4 hours, until the chicken is tender and shreds easily.
Shred: Use two forks to shred the chicken directly in the slow cooker and stir well to coat it in the flavorful sauce. Keep warm until ready to serve.
Serve: Enjoy over mashed potatoes, rice, or egg noodles.