Wash and clean the vegetables and cut into bite-sized pieces. Brush and quarter the mushrooms, peel the onion, halve and cut into thin half rings, peel the garlic and chop finely. Pluck the rosemary needles from the branch and also finely chop. Crumble the feta and mix all the ingredients together in a bowl. Cover everything for 2 - 3 hours and let it steep in a cool place.
Then distribute the mixture over eight pieces of aluminum foil, seal the packets and grill over indirect heat for about eight minutes.
Serve as a vegetarian dish with baguette or as an accompaniment to grilled meat.