In a nonstick skillet, toast the quinoa and cumin over medium heat until the quinoa is golden-brown, 3 to 5 minutes.
In a pan, boil 2 cups water. Add the quinoa; lower the heat. Cover and simmer until the water is absorbed, 15 minutes. Fluff with a fork; let cool.
Meanwhile, in a bowl, whisk the onion, oil, soy sauce, vinegar and 1/2 tsp. salt.
Transfer the quinoa to a serving bowl. Fold in the vinaigrette, tomato, cucumber, arugula and pine nuts.