1. Prepare the marinade. Heat oil over medium-high heat. Add scallions, ginger, and garlic and cook, stirring, until softened, about 3 minutes. Remove from heat and add pineapple (with the juice), orange juice, lemon juice, hoisin sauce, soy sauce, brown sugar, and red pepper flakes and stir well to combine. Reserve half the marinade in a container and refrigerate. Place the remaining marinade in a large, resealable plastic bag with the ribs. Turn to coat the ribs, and refrigerate overnight.
2. When ready to cook the ribs, preheat oven to 325degreesF. Spray a roasting pan with vegetable cooking spray. Remove ribs from bag and place in the pan, pouring marinade from bag on top. Roast, uncovered, until the meat is tender, about 90 minutes. Ten minutes before the ribs are ready to come out of the oven, preheat grill to medium heat.
3. While ribs are in the oven, make the grill sauce. Pour the reserved marinade into a small saucepan, bring to a boil over high heat, then lower heat and simmer until the sauce is reduced by about 1/3 and slightly thickened, about 5 minutes. Transfer to a blender and blend until smooth, about 30 seconds (the sauce will be thick). Alternately, use an immersion blender.
4. Transfer ribs to the preheated grill and cook, covered, turning once and brushing with the grill sauce, for about 5 to 7 minutes per side, or until the outside begins to caramelize. Let the meat rest for 5 minutes, then serve with remaining sauce on the side and grilled pineapple slices, if desired.
Source: fresh magazine July, August 2010