Boil a pot of water in a medium saucepan. Meanwhile, heat a grill pan.
Parboil the baby potatoes for 10 minutes. about 8-9 minutes into boiling the potatoes, add in the brussel sprouts and boil for another 2 min. Drain and cool for 5 minutes.
Thread the potatoes, brussel sprouts, mushrooms, onions, and zucchini.
Drizzle the veggies with a little olive oil, salt, and pepper.
Grill for 5 minutes per side.
Meanwhile, in a small bowl, whisk together the mustard sauce ingredients.
Drizzle the veggies withbthe mustard sauce and enjoy.