Cut all vegetables into medium-sized cubes and put them in a large roaster or baking tray, along with the other ingredients (olive oil, salt, pepper, thyme, tarragon, fennel, parsley and mustard). Add water until covered.
Preheat the oven to 180 degrees Celsius and place the roaster or baking tray covered for 1 hour. Then, uncover your utensil, add as much water as needed and bake for half an hour at 200 degrees Celsius. Finally, add more water if needed and continue baking at 200 degrees for 20 minutes.
Once you take the food out of the oven, you can serve it with the tahini sauce — either on top of the vegetables or next to them like a delicious dip!