Season the chicken breasts with salt, black pepper, garlic powder, and onion powder. Place them in the slow cooker.
In a separate bowl, whisk together the chicken broth, cream of chicken soup, thyme, rosemary, and Worcestershire sauce. Pour this mixture over the chicken in the slow cooker.
Cover and cook on low for 6-7 hours or on high for 3-4 hours, until the chicken is cooked through and tender.
If you prefer a thicker gravy, mix the cornstarch with water in a small bowl until smooth. Stir this mixture into the slow cooker during the last 30 minutes of cooking.
Once done, shred the chicken with two forks and mix it with the gravy before serving.