Position the rack in the center of the oven and heat the oven to 400°F.
Warm 1 tablespoon of the oil in a medium sauce pan set over medium heat. Add the quinoa and cook, stirring often, until lightly toasted, about 2 minutes. Pour in 1½ cups water, raise the heat to high, and bring to a boil. Cover, reduce the heat to low, and simmer slowly until the water has been absorbed, about 15 minutes. Remove from the heat and set aside, covered, for 10 minutes. Fluff with a fork, spread on a large plate, and refrigerate for at least 30 minutes or up to 4 hours.
Toss the sweet potato cubes with 1 tablespoon of the olive oil on a large rimmed baking sheet. Bake until golden brown, stirring once, about 30 minutes. Cool on the baking sheet for 20 to 30 minutes.
Whisk the remaining 2 tablespoons of oil with the vinegar, salt, and pepper in a large salad bowl. Add the arugula, pears, onion, parsley, and mint, as well as the chilled quinoa and sweet potatoes. Toss gently but well to serve.
