Place turkey breast into a large slow cooker. Whisk onion soup mix and water in a bowl and pour the mixture over the turkey breast, spreading it out to evenly cover the meat.
Stir garlic powder, onion powder, parsley, seasoned salt, basil, and oregano in a bowl until thoroughly combined; sprinkle the seasonings over the turkey breast.
Cook on Low until turkey is very tender and the seasonings have flavored the meat, 8 to 9 hours. An instant-read meat thermometer inserted into the thickest part of the breast, not touching bone, should read at least 165 degrees F (75 degrees C).