POUR 2 cups of the dressing (or 1 cup of the dressing for trial recipe) over meat in shallow nonreactive pan; turn meat over to coat both sides with dressing. Cover and refrigerate at least 2 hours or overnight to marinate, turning occasionally.
REMOVE meat from marinade; discard marinade. Place meat in full-size hotel pan (or half-size hotel pan for trial recipe). Cover with foil.
BAKE in 275°F-standard oven for 2-1/2 hours (or in 250°F-convection oven for 1-1/2 hours) or until meat is tender and cooked through (160°F). Drain excess liquid.
POUR barbecue sauce over meat. Continue baking 30 min., basting occasionally with the liquid in bottom of pan. Meanwhile, grill onions over medium heat about 5 min. or until tender, turning and brushing occasionally with the remaining 1/2 cup dressing (or 1/4 cup dressing for trial recipe). Cut meat diagonally across the grain into thin slices.
FOR each serving: Fill 1 roll with about 5 oz. of the meat mixture and about 1/4 cup of the onions.