Prepare the marinade by combining the oil, vinegar, garlic, mustard, and spices in a large stainless steel bowl. Toss in zucchini, peppers and onion. In a pot of boiling water, cook the potatoes for 10 minutes until slightly tender. After 5 minutes, add the carrots (so that they cook 5 minutes); after 7 minutes add the eggplant (so it cooks 3 minutes). Drain the pot and add the potatoes, carrots, and eggplant to the marinade. Put all the vegetables on skewers, and then grill over medium heat until they are cooked through. You can occasionally baste the vegetables with more of the grilling sauce but do this sparingly or it will slow the cooking process.