Preheat oven to 375°F (190°C).
Rinse quail and pat dry. Using kitchen shears, cut along both sides of backbone and remove. Pry open and make 1-inch (2.5 cm) incision at top into breastbone. Flatten with heel of hands; place in large shallow glass baking dish.
In small bowl, whisk together hoisin sauce, vinegar, soy sauce, ginger, garlic and five-spice powder. Brush over both sides of quail; cover and refrigerate for at least 1 hour or for up to 8 hours, turning occasionally.
Reserving marinade, transfer quail to rack in roasting pan; roast, brushing once with marinade, in oven for about 25 minutes or until juices run clear when pierced.
Meanwhile, in small saucepan over medium-high heat, bring remaining marinade and
1/4 cup (50 mL) water to boil; boil gently for 5 minutes. Brush sauce over quail before serving.