To prepare dressing, combine first 6 ingredients in a small bowl; stir with a whisk until well blended.
To prepare salad, place quinoa in a large nonstick skillet; cook 4 minutes over medium heat, stirring frequently. Place quinoa in a fine sieve; place sieve in a large bowl. Cover quinoa with water. Using your hands, rub grains together for 30 seconds; rinse and drain. Repeat procedure twice. Drain well.
Combine quinoa, 2 3/4 cups water, and 1/2 teaspoon salt in a large saucepan; bring to a boil. Cover and reduce heat; simmer 20 minutes or until liquid is absorbed. Remove from heat, and cool to room temperature. Stir in dressing, onions, and the remaining ingredients. Cover and chill.