Rinse quinoa thoroughly under cold running water. In a pot combine 1 cup quinoa, a pinch of kosher salt, and 2 cups water and bring to a boil. Reduce heat to medium-low, cover, and simmer until quinoa is tender, about 10 minutes. Remove from heat and let stand, covered, for 5 minutes.
Fluff the quinoa with a fork and spread it out on a baking sheet to cool slightly, about 10 minutes.
Meanwhile, in a large bowl whisk together 1/4 cup olive oil, 3 tablespoons white balsamic vinegar, 1 1/4 teaspoons kosher salt, 1/4 teaspoon freshly ground black pepper, and the finely chopped shallot to make the dressing. Once the quinoa has slightly cooled, add the quinoa, halved cherry tomatoes, 1 cup crumbled feta, 1/2 cup freshly chopped mint leaves, and 1 cup arugula to the bowl and toss to combine. Taste and adjust seasoning as needed.