If using wooden skewers, soak skewers in water for at least 15-30 minutes.

Boil potatoes in pot of water for 10-15 minutes or until they can easily be pierced by fork but not mushy. Meanwhile, whisk vinegar, celery salt, honey, dried dill, and mustard together in a bowl. While whisking, slowly add olive oil. Set aside.

Place softened potatoes and raw zucchini cubes in shallow pan or large resealable bag and add vinaigrette mixture on top. Mix together and allow to marinate at least 15 minutes in refrigerator. Meanwhile, preheat grill to 350ºF or grill pan over stovetop to medium-high heat.

Thread vegetables onto wooden or metal skewers, alternating between potato and zucchini slices. Grill each skewer for about 2-3 minutes on each side or until dark grill marks appear. Place on serving dish and set aside.

Whisk mayonnaise and milk together. Drizzle skewers with mayonnaise sauce. Garnish with green onions and other mix-ins/toppers (if using). Serve immediately.