With a sharp knife, cut a deep pocket between each rib on meaty side of roast. Combine the green pepper, green onions, celery and garlic; stuff deeply into pockets. Season roast with salt and cayenne pepper.
Place roast, rib side down, in a shallow roasting pan. Bake, uncovered, at 350° for 1 hour 40 minutes or until thermometer in the pork reads 145°. Let stand for 15 minutes before carving.