Halve ribs lengthwise and dredge in flour. Heat a large skillet over medium-high heat and add vegetable oil. Add ribs to skillet and sear on all sides until deep golden brown, about 2 to 3 min. per side. Cook in batches to avoid overcrowding skillet. Add ribs to slow cooker along with white parts of scallions, garlic, rice vinegar, sherry, honey, soy sauce, Chinese Five Spice, Crushed Red Pepper Flakes, and orange zest. Stir, cover, and set slow cooker to low for 7 hours or high for 3 to 3 1/2 hours. When ribs shred easily with a fork, transfer them to a plate. Transfer sauce in slow cooker to a large skillet. In a small bowl, combine orange juice and corn starch to make a slurry. Add to sauce and bring to a simmer, stirring for 2 to 3 min. or until sauce thickens. Glaze pork with sauce, garnish with green parts of scallions and serve immediately.