In resealable food-storage plastic bag or 13x9-inch (3-quart) glass baking dish, place pork pieces. Pour soy sauce over pork; toss to coat. Seal bag or cover dish. Let stand at room temperature 15 minutes to marinate, turning or stirring occasionally.
Meanwhile, heat gas or charcoal grill. In small bowl, mix plum sauce, orange peel, gingerroot and red pepper flakes; set aside. Cut green onions into 1-inch pieces. Cut each pineapple spear into 6 pieces.
Alternately thread pork, onion (skewered crosswise) and pineapple evenly onto 4 (12- to 15-inch) metal skewers; discard marinade.
When grill is heated, carefully oil grill rack; place kabobs on gas grill over medium-high heat or on charcoal grill over medium-high coals. Brush plum sauce mixture over kabobs; cover grill. Cook 5 minutes. Turn kabobs; brush with sauce mixture. Cook covered 4 to 6 minutes longer, brushing frequently with sauce mixture, until pork is no longer pink in center. Discard any remaining sauce. If desired, serve with hot cooked instant white and wild rice.