Sage and Onion Stuffed Pork Loin

boneless pork loin (about 3-4 lbs)

Stuffing:

slices white bread

small onion, finely chopped

finely chopped sage leaves -OR- 1 tsp ground sage -OR- 1 tsp poultry seasoning

chopped fresh parsley -OR- 1 tbs dehydrated (optional)

salt

white pepper

butter