Cut the oranges into segments, removing the surrounding membranes (see Shortcut, below). Squeeze the membranes over a bowl to catch their juices.
Heat the oil in a large skillet over medium heat. Add the ginger and cook, stirring occasionally, for 2 minutes.
Sprinkle the halibut with 1/2 teaspoon salt, 1/4 teaspoon pepper, and the cumin. Cook for 4 minutes. Turn, add the scallions and oranges with any liquid, and continue cooking until the fish is the same color throughout and flakes easily, 4 to 5 minutes.
Cook the pasta according to the package directions while the halibut cooks.
Divide the pasta and fish among individual plates. Spoon the oranges and sauce over the top and sprinkle with the cilantro.
Shortcut: To section an orange and remove its membranes without making a mess, cut away the peel and white pith with a knife. Then, working over a bowl, with the orange in one hand, make a cut on either side of each segment, inside its surrounding membrane. The sections will be free in no time.