Preheat barbecue to medium-high heat. Remove plastic lid from potato griller container. Pour in 1 1/2 cups (375 mL) cold water. Cover with foil and seal edges. Place on barbecue and cook 25 to 30 min., until fork tender. (If using bagged mini potatoes, quarter potatoes. Place in 3-cup (750 mL) foil container and follow instructions above.)
While potatoes cook, make Lemon Parsley Vinaigrette by whisking together olive oil, lemon juice, mustard, salt and pepper. Stir in parsley. Set aside.
Remove potatoes from barbecue and carefully remove foil. Drain any remaining water. Keep grill heated.
Toss potatoes with 2 tbsp (30 mL) of vinaigrette (reserve the rest). Cover and keep potatoes warm.
Toss shrimp with the 1 tbsp olive oil and Old Bay Seasoning. Grill shrimp 2 to 3 min. per side until pink and just cooked through. Grill zucchini for 2 min. per side, or until tender-crisp and grill-marked.
Combine potatoes, shrimp and zucchini in large bowl. Toss with reserved vinaigrette.