Turn on the oven to a medium heat.
Peel the mushrooms and break them into chunks. Rinse the potatoes, cut the big ones in half. If you don't have baby potatoes, you can use regular ones, and cut them into quarters. Chop the onion and put it in the cooking bag together with crushed garlic and parsley leaves.
Put all the other ingredients in the cooking bag. Toss everything, so the spices and the olive oil will coat the vegetables. Take the air out of the bag, tie it and make a few holes in it. Put the cooking bag on an oven tray and set it in the middle of the oven. Bake in an oven for one hour or until done. After half an hour, if possible, turn the bag to the other side, or shake the tray to mix the potatoes a bit. When done, garnish with some fresh parsley and olive oil.