1. Combine first 3 ingredients and 1/4 teaspoon crushed red pepper in a bowl. Set aside.
2. Drain pineapple, reserving 1/4 cup juice. Combine reserved juice, 6 tablespoons stock, ketchup, next 3 ingredients, and remaining 1/4 teaspoon crushed red pepper in a small bowl, stirring until sugar dissolves. Combine cornstarch and remaining stock in another small bowl.
3. Heat oil in a large nonstick skillet over medium-high heat. Stir-fry pork mixture in hot oil 5 minutes or until pork is done. Remove pork from pan; keep warm. Add onion, bell peppers, and water chestnuts to pan; stir-fry 3 minutes or until crisp-tender. Add ketchup mixture. Bring to a boil; stir in cornstarch mixture, pineapple chunks, and pork mixture with any accumulated juices. Cook 2 minutes or until sauce thickens. Serve immediately over rice. Garnish with green onion slices, if desired.