Preheat oven to 400°. Place asparagus, tangerine sections, fennel and mint in a 9- by 13-inch baking dish. In a small bowl, whisk together olive oil, lemon juice, pepper and mustard. Pour the olive oil mixture over asparagus, tangerines, fennel and mint and coat evenly.
Roast about 10–12 minutes, until crisp tender, stirring midway. Baking time will depend on thickness of asparagus. Remove mint sprigs after baking.
Transfer asparagus and other ingredients to a serving platter and drizzle with tangerine-infused balsamic vinegar. Garnish with fresh mint and pistachio pieces, if desired.
Variation: Extra-virgin olive oil and balsamic vinegar can be substituted for the flavor-infused varieties.