Preheat oven to 220 C (430 F).
Cut the fennel, parsnip and mushrooms in two and cover in oil. Mix with salt, pepper, garlic, whole thyme and rosemary in the oven (apart from the mushrooms) in a tray for 30-45 min.
While the vegetables are in the oven: Remove the fat from the lamb and place in a container/plastic bag/Waxed bag. Add olive oil and a few sprigs of thyme, rosemary and the mushrooms. Mix in the bag and store in the fridge until you have finished the vegetables.
Take out and let cool. After it has cooled enough, place in the bag with the lamb and place in the fridge overnight.
On the fire:
Make sure you have a lot of hot coal before starting. So plan the fire to burn a while, until the coals are hot enough, there are no more flames and you have enough coal so they don't die down before you have finished grilling. You can also relight the fire with the coals after you have finished cooking. Place the grill over the coals, take out the lamb and place on the grill after the grill has heated up. Depending on how thick the lamb is, grill until the meat is a little more firm, about 5 min on each side. After the first five minutes, you can place the vegetables on. When the lamb is almost cooked, take it off the grill and let rest for a few minutes, while the vegetables heat up a bit more or are ready to take off. Serve on a plate and enjoy!
Watch the video of the cooking adventure here: