Place the quinoa in a fine mesh strainer and rinse under running tap water. Fill a medium saucepan about ¾ full with water. Bring to a boil and stir in the quinoa. Cook for 12 minutes or until quinoa is tender (Germ spirals should just be coming away from the seed).
Drain the quinoa in a fine mesh strainer, then transfer back to the same pot you cooked it in and cover tightly with a lid off of the heat. Let the quinoa steam for about 10 minutes.
Fluff with a fork and let the cooked grains cool to room temperature before assembling the salad. To speed up this process, pour the quinoa onto a sheet pan and spread into an even layer. Excess moisture will evaporate and the quinoa will cool and dry in about 10 minutes.
Meanwhile, prepare the vegetables, slicing the onions, scallions, radish, parsley and mint and transferring them to a large bowl.
In a small bowl or glass measuring cup, add the lemon juice, zest, garlic, dijon mustard vinegar, salt and pepper. Whisk in the olive oil in a steady stream until emulsified.
When quinoa is cool, fluff the quinoa with a fork and add it to the vegetables and gently toss together.
Add the vinaigrette and toss to combine. Can be made ahead and served chilled or at room temperature.