Cut pork into 3 chunky strips about 2 inches thick and 6 inches long. Set aside.
In large bowl, combine the garlic, five spice powder, sugar, sesame oil, soy sauce, ketchup, and hoisin. Reserve 2 tbs of marinade for brushing.
Add the pork to the marinade and coat well. Marinate for 1 to 24 hrs, turning 2-3 times.
To grill the pork, set grill to medium. Lightly oil grates and cook for 16-20 minutes turing frequenly. During the last 5 minutes, baste with reserved marinade. Cool on coolng rack. If roasting, preheat oven to 475 and roastin top third of oven for 30-35 minutes. Baste with marinade every 10 minutes. Regardless of cooking method, the xa xiu should have a glazed look with charred exterior and internal temperature of 145F. Allow to rest for 10 minutes before slicing into banh mi.