I love the ease of cooking in my crockpot, and could not believe how well this turkey turned out! I got a smaller whole (bone-in) turkey instead of a boneless turkey breast, so either will work depending on store availability or personal preference.
5 lb frozen boneless turkey breast, thawed
1/4 cup butter, softened
3 tbsp Italian seasoning
1 tbsp garlic salt
1 cup sliced yellow onion
Rub turkey breast with butter; sprinkle with Italian seasoning and garlic salt. Arrange onion slices in an even layer in a 5-7 quart slow cooker. Pour 1 cup water over onion; place turkey breast over onion. Cover and cook on low 7-8 hours; let stand 10 minutes before slicing.