Begin by seasoning the turkey breast. Rub the olive oil all over the turkey, then sprinkle the salt, pepper, garlic powder, onion powder, thyme, and rosemary evenly on all sides.
Place the sliced onion, chopped carrots, and chopped celery at the bottom of the crockpot to create a flavorful bed for the turkey.
Pour the chicken broth and apple juice (if using) over the vegetables in the crockpot.
Carefully place the seasoned turkey breast on top of the vegetables in the crockpot.
Cover the crockpot with the lid and set it to cook on low for 6 hours, or on high for about 3 to 3.5 hours.
After cooking, use a meat thermometer to check the internal temperature of the turkey, which should read at least 165°F.
Once fully cooked, remove the turkey breast from the crockpot and let it rest for about 10 minutes before slicing.
Serve the turkey breast with the cooked vegetables and spoon some of the broth over for added flavor.