Pat the turkey breast dry
Season with salt, pepper, and any desired herbs or spices
Place chopped onions, garlic, or vegetables in the slow cooker if desired
Add a small amount of broth, water, or wine to the bottom of the slow cooker
Put the turkey breast into the slow cooker, skin side up if applicable
Cover and cook on low for 5 to 7 hours, or until the internal temperature reaches 165°F
Avoid lifting the lid during cooking
Check the temperature in the thickest part of the breast with a meat thermometer
Remove the turkey breast from the slow cooker when done
Let it rest for 10 to 15 minutes before slicing
Slice against the grain and serve
Optionally, use the cooking liquid to make gravy