Meanwhile, to prepare the dressing: Whisk together the olive oil, lemon juice, garlic, mustard, salt and red pepper flakes. Season to taste with freshly ground black pepper.
To cook the quinoa: Combine the rinsed quinoa and 2 cups water in a medium saucepan. Bring the mixture to a boil over medium-high heat, then decrease the heat to maintain a gentle simmer. Cook until the quinoa has absorbed all of the water, about 15 minutes, reducing heat as time goes on to maintain a gentle simmer. Remove from heat, cover, and let the quinoa rest for 5 minutes, which gives it time to fluff up.