I put the loin in a cooking bag(like you cook a turkey in)then pour a package of onion soup mix over top, add a 1/2 cup hot water close bag and bake at 350 degrees until tender. I have an electronic thermometer that beeps when the meat gets to a certain temperature so I can't tell you exactly how long to cook it. It depends on the size of the pork loin.
We love it this way, I usually don't have any leftovers to put up.