Preheat grill to medium-high.
Brush zucchini and asparagus with 2 tablespoons vinaigrette and sprinkle with ⅛ teaspoon each salt and pepper. Drizzle salmon with 2 teaspoons vinaigrette and sprinkle with the remaining ⅛ teaspoon each salt and pepper.
Place the vegetables and the salmon pieces, skin-side down, on the grill. Grill the vegetables, turning a few times, until tender, 6 to 8 minutes. Grill the salmon, without turning, until it flakes with a fork, 8 to 10 minutes.
Cut the vegetables into 3 or 4 pieces and place in a medium bowl. Drizzle with 2 tablespoons vinaigrette and toss to coat. Remove the skin from the salmon, if desired; serve the salmon alongside the vegetables. Drizzle the salmon with 1 tablespoon vinaigrette, if desired. (Refrigerate any remaining vinaigrette for up to 3 days.)
