Advance Preparation: Orange and Hoisin sauce can be made 1 day in advance. Cover and refrigerate.
Preheat oven to 350°F.
Place a long sheet of heavy-duty foil on each of 2 large-rimmed baking sheets extending foil over the short edges. Salt and pepper both sides of the ribs and place rack of ribs centered on foil concave side up.
Pour ½ cup orange juice over each rib rack. Fold up foil to seal packets. Bake until ribs are tender, about 1.5 to 2 hours.
Meanwhile, whisk together the next eight ingredients along with the orange zest in a small saucepan. Bring sauce to a boil, reduce heat and simmer until sauce is thickened, about 15 minutes.
Prepare baking sheets: Line two large-rimmed baking sheets with parchment or aluminum foil and place a baking rack in each.
When the ribs have finished cooking, remove the foil and arrange each rack of ribs on the racks on the baking sheets.
Set the oven heat to broil.
Brush one side of the ribs generously with the hoisin orange sauce and transfer on backing sheet to the oven and broil on the top oven rack for 5 to 7 minutes until the sauce is caramelized and browned. Remove from the oven and flip each rack over. Brush with more sauce and return to the oven for 5 to 7 minutes. (Turn rib racks over and repeat again if desired.)
Use a large knife to cut between the ribs. Mound on a platter and sprinkle with green onions. Serve immediately.