Preheat the oven to 400°. In a large saucepan, heat 1 tablespoon of the olive oil. Add the quinoa and toast over moderate heat, stirring, for 2 minutes. Add 3 cups of water, season with salt and bring to a boil. Cover and simmer the quinoa for 16 minutes. Remove from the heat and let stand for 10 minutes. Fluff the quinoa, spread it out on a baking sheet and refrigerate until it is chilled, about 20 minutes.
Meanwhile, on a baking sheet, toss the sweet potatoes with 1 tablespoon of the olive oil and season with salt and pepper. Roast for about 25 minutes, stirring once, until golden and softened. Let cool.
In a large bowl, whisk the remaining 6 tablespoons of olive oil with the vinegar; season with salt and pepper. Add the quinoa, sweet potatoes, apples, parsley, onion and greens and toss well. Serve right away.