Place the quinoa and 2 cups water in a small saucepan. Bring to a boil over high heat. Stir once, cover and reduce the heat to low. Continue to cook until the water is absorbed and the quinoa is tender, about 20 minutes. Remove from the heat and let stand 5 minutes, uncover and fluff with a fork.
Meanwhile, heat 1 teaspoon of the sesame oil in a medium nonstick skillet over medium-high heat. Add the garlic and cook until fragrant, about 1 minute. Add the mushrooms and continue to cook, stirring, until the mushrooms are tender, about 5 minutes. Add the snow peas, 1/4 teaspoon salt and 1/4 teaspoon pepper. Cook, stirring, until bright green but still crisp-tender, about 3 minutes. Remove from the heat. Combine the cooked quinoa, mushroom mixture, soy sauce, scallions and remaining 2 teaspoons sesame oil in a medium bowl. Toss gently to combine. Season with additional salt and pepper. Serve warm or at room temperature.