In a small mixing bowl, combine the mayonnaise, Dijon, garlic, tarragon, capers, and shallots. Mix well. Fold in the crabmeat. Season with salt and pepper. Set aside. In another mixing bowl, combine the asparagus and the onion. Season to taste with the olive oil, balsamic vinegar, and salt and pepper. To serve, divide the asparagus mixture between four plates and mound the crab salad in the center of each plate. Lay 3 zucchini flowers over the crab salad. Garnish with parsley.