Pomegranate Sumac Dressing

¼ cup red onion, minced • 1 tablespoon fresh lemon juice • 2 tablespoons red wine vinegar • ? cup pomegranate seeds • ¼ cup fresh mint leaves, thinly sliced  • 1 tablespoon sumac (a tangy spice that can be found in most stores) • ¼ teaspoon sea salt  • ¼ teaspoon freshly ground black pepper