Put the onion and tomato quarters on skewers, then place them on a large plate with the mushrooms and the zucchini halves. Drizzle with olive oil, then season to taste with oregano, salt and pepper.
Preheat barbecue to medium heat. Thoroughly clean the rack when it is hot, then place the vegetable skewers, mushrooms, zucchini halves and duck sausages on it. Grill 12-15 minutes, turning a few times.
When the vegetables start to turn golden brown but are still crispy, remove them from the grill with the duck sausages, and serve immediately on a large serving dish. Serve with the creamy cranberry mustard.
Put all the ingredients in a small bowl and season to taste with salt and pepper. Whisk well and cover. Let rest for at least 1 hour to allow the flavours to meld. Complements grilled meats marvellously.
Recipe developed by Nicolas Vallée, professional chef