To make Rosemary-Dijon Vinaigrette: Whisk together vinegar, mustard, shallots, lemon juice, and lemon zest in small bowl. Slowly whisk in olive oil until mixture thickens or emulsifies. Stir in rosemary, and season with salt and pepper, if desired. Set aside.

To make Vegetable Skewers: Cook potatoes 3 minutes in large pot of boiling salted water. Add sugar snap peas, and cook 1 minute more, or until sugar snap peas are crisp-tender. Drain vegetables, and rinse under cold water. Drain once more, and pat dry.

Toss potatoes, sugar snap peas, mushrooms, red bell pepper, red onion, yellow squash, and zucchini with 1/2 cup Rosemary-Dijon Vinaigrette. (Reserve remaining Rosemary-Dijon Vinaigrette for another use.) Cover, and refrigerate 1 hour, or overnight.

Preheat grill to medium-high heat. Thread vegetables onto 12 presoaked bamboo skewers, leaving 1/4-inch space between each one to ensure even cooking.

Rub grate or vegetable grill topper with vegetable oil. Grill skewers 3 to 4 minutes per side, or until vegetables are slightly charred and soft. Season with salt and pepper, if desired, and drizzle with remaining 1/4 cup Rosemary-Dijon Vinaigrette.