Place the quinoa in a fine mesh strainer and rinse under running tap water. Transfer quinoa to a saucepan and add 2 cups water. Bring to a boil, cover and reduce heat to a simmer. Cook for 15 minutes or until quinoa is tender and spirals are visual on the surface. Remove from heat and let sit uncovered, until quinoa is at room temperature.
Meanwhile, prepare the vegetables, slicing the onions, scallions, radish, parsley and mint and transferring them to a large bowl.
In a small bowl, add all the ingredients for the vinaigrette and stir to combine.
When quinoa is cool, fluff the quinoa with a fork and add it to the vegetables. Add the vinaigrette and toss to combine. Can be made ahead and served chilled or at room temperature.