Rinse quinoa in a fine mesh strainer; drain well. Bring broth and quinoa to a boil in a medium saucepan; reduce heat and simmer, covered, for 12 minutes. Remove from heat and let stand for 10 minutes, then fluff with a fork and let cool. Transfer to a large bowl. Whisk together all dressing ingredients in a medium bowl and pour over quinoa; stir well to coat. Add grapes, onion, cilantro, and jalapeno pepper; cover and chill for at least 1 hour. Lightly stir in avocado and transfer to a decorative bowl. Sprinkle with nuts, if desired.