Place pork roast on a rack in a shallow roasting pan. Insert an oven-safe meat thermometer into the roast. Season meat with salt and pepper. Arrange onion slices on top of roast. Roast, uncovered, in a 325 degree F oven for 1-1/4 to 1-1/2 hours or until the meat thermometer registers 155 degree F.
Transfer roast to a serving platter; cover meat with foil and let it stand 15 minutes for easier carving.
Slice pork roast. Serve with Red Cabbage and German Potato Salad, if desired. Makes 8 servings.