Heat oven to 425°F.
Toss the sweet potatoes, parsnips, and red onion with 2 tablespoons of the olive oil and 1 teaspoon of the salt and spread evenly onto two half-sheet pans. Roast for 15 minutes, then toss the vegetables, rotate the pans, and roast until the vegetables are tender and golden brown, about another 10 minutes. While the vegetables are roasting, prepare the quinoa.
Bring 2 cups of water and 1/2 teaspoon of kosher salt to a boil in a 2-quart saucepan. Whisk the rinsed quinoa into the boiling water, add the cinnamon, cover, reduce the heat to low, and simmer for 15 minutes. Remove from the heat and cool covered for 5 minutes. Fluff with a fork.
Combine the remaining olive oil, apple cider vinegar, maple syrup, mustard and salt in a small canning jar or other sealable vessel. Cover and shake like a martini to emulsify. (But don't use your cocktail shaker...you don't want to get fat in there.)
Toss the warm vegetables, quinoa, herbs, and dressing together in a large bowl. Add the apple and pepitas just before serving warm or at room temperature.