Spread pork flat; sprinkle lightly with salt.
Heat water to boiling; add onions.
Cook 5 minutes; drain.
Mix onions and remaining ingredients.
Spread onion mixture on pork; roll up.
Fasten with metal skewers.
Place pork fat side down on rack in shallow roasting pan.
Spoon any remaining stuffing over top of pork.
Insert meat thermometer so tip is in center of thickest part of pork and does not rest in stuffing.
Roast uncovered in 325° oven until thermometer registers 170°, 3 to 3 1/2 hours.