Trim fat from pork. Place pork in a self-sealing plastic bag set in a shallow dish. For marinade, in a small bowl combine soy sauce, catsup, and garlic powder. Pour over pork; seal bag. Marinate in the refrigerator for 4 to 24 hours, turning bag occasionally.
Drain pork, discarding marinade. Place pork on a rack in a shallow roasting pan. Roast in a 425 degree F oven for 20 to 30 minutes or until done (160 degree F). Sprinkle sesame seeds on a piece of foil; carefully roll pork in sesame seeds. Makes 4 servings.