Place all vinaigrette ingredients in a jar with a tight-fitting lid. Shake well, then refrigerate until ready to serve.
To prepare pickled onions, stir together vinegar, sugar and salt in a medium bowl. Add onion and stir well to coat. Cover and refrigerate for at least 30 minutes to marinate.
Bring stock and quinoa to a boil in a small saucepan. Reduce heat and simmer, covered, for 12 minutes. Remove from heat and let stand for 10 minutes. Remove cover and fluff with a fork; let cool.
Stir together walnuts and goat cheese in a small bowl and roll into quarter-size balls.
To assemble Buddha Bowls, place equal amounts of arugula into 4 large salad bowls and top with equal amounts of quinoa. Place dried apricots and dried apples off to one side and the cheese walnut balls on the opposite side. Top with pickled onions and drizzle with vinaigrette.