In shallow Dutch oven, heat oil over medium-high heat; brown chicken, in batches if necessary. Spoon off fat.
Add stock, soy sauce, sugar, two-thirds of the onions, the garlic, ginger, cinnamon, cloves and pepper; bring to boil. Cover and simmer over medium-low heat for 25 minutes or until juices run clear when chicken is pierced.
Increase heat to high and return chicken mixture to boil. Stir in bok choy; cook for 2 minutes. Dissolve cornstarch in 2 tsp water; add to pan and cook, stirring, for 1 minute or until thickened and bok choy is tender-crisp. Serve sprinkled with remaining green onions.