Top 4 slices whole-grain artisan bread with grated Parmigiano-Reggiano cheese; place on rimmed baking sheet. Arrange asparagus around bread; brush with extra-virgin olive oil. Broil 1 to 2 minutes or until cheese is melted and bread is lightly toasted; remove bread. Continue broiling asparagus 1 to 2 minutes or until crisp-tender.
Meanwhile, combine 2 tablespoons mayonnaise with 3/4 tablespoon chopped fresh tarragon and 1/2 tablespoon sliced green onion. Spread over un-toasted side of two slices of bread. Top with asparagus; sprinkle with coarse sea salt and pepper. Top with remaining bread, Parmesan-side up.
PER SERVING: 330 calories, 19 g total fat (4.5 g saturated fat), 14 g protein, 27 g carbohydrate, 15 mg cholesterol, 580 mg sodium, 5 g fiber