Dust and season the cut oxtails all around with flour, salt and pepper.
Heat oil over medium-high heat in a Le Creuset or other enameled braising pot. Color oxtails on all sides and remove from pot. Discard oil and wipe clean. Add 2 tablespoons oil and roast oranges on both sides, remove when well caramelized on both sides. Roast maitake, ginger and whole shallots in the same pot until they color slightly and begin to soften. Deglaze with red wine and Worcestershire sauce, reduce by 1/2. Add the oxtails and oranges back to the pot. Add enough water to cover half the oxtails. Cover and cook in a 300 degree oven until falling of the bone.
Strain off the sauce and reduce by half or until thick enough to coat the back of a spoon.
Fold the braised ingredients and scallions together and serve.