Slice all the vegetables round using a mandoline slicer or with a knife. Slice potato in 1/4 inch thickness and zucchini and eggplant in 1/2 inch thickness.
Slice tomatoes and onions too. Always keep sliced eggplant and potato in water to prevent oxidation.
In a bowl add olive oil, oregano, dried thyme, fresh parsley, pepper, salt, and give a stir. Keep aside.
Stir the oil in potatoes, eggplant, and zucchini. Do not season onion and tomatoes.
On a baking tray pour the diced tomatoes. Arrange the vegetables in order or just throw them randomly. Pour some diced tomatoes on top too(optional).
Pour the remaining oil on top of the vegtables and cover it in a foil and prick some holes on top and bake for 30 minutes at 450°F in a pre-heated oven.
Remove the foil and bake for another 30 minutes. Broil for few minutes if you want to change the color on top.
Notes
Do not soak onion and tomato in an olive oil dressing.