Roasting vegetables without oil is known as dry roasting, and it's a common cooking tool used in Asian soup stocks and Middle Eastern dishes. Hard, root vegetables such as potatoes, carrots and turnip do well in an Asian dry-roasting scenario, where softer-skinned vegetables roast better in an oven, Middle Eastern-style, as do onions and garlic.
Dry roasting, Middle Eastern Style
Preheat the oven to 450 degrees F. Wash the eggplant, and prick it all over with a fork.
Place the eggplant, head of garlic and onion onto a baking tray. Put it in the preheated oven.
Roast the eggplant for 10 minutes, then rotate so it chars on 2 sides of the eggplant. Roast for another 10 minutes, or until the inside of the eggplant seems soft. The onion and garlic will have roasted inside their own skin, and will be soft inside. This is a good method to take out the harshness of onion and garlic while retaining its flavor.
Make babaganoush, a Middle Eastern eggplant dip, by halving the eggplant after it cools, scooping out the flesh, and mixing the eggplant with garlic, salt, pepper, tahini (a sesame paste) and fresh parsley or mint. Add olive oil for a smooth texture.
Dry Roasting Asian Style
Take a carrot or other root vegetable and wash it thoroughly. Peel the outer layer of the root vegetable, and chop roughly, either in half or quarters.
Heat a saucepan on medium heat. Run your fingers under tap water, then flick some water into the saucepan. If the water sizzles and evaporates, it is hot enough.
Put the chopped root vegetables into the saucepan. Take a pinch of salt and drizzle it onto the vegetables.
Turn the heat down and cover the saucepan. The heat and the salt will bring some water out of the vegetables, and they will begin to cook slightly.
After 3 to 5 minutes, uncover the saucepan. Let the root vegetables dry roast in the pan, browning before you turn them. To create a broth, add water after the vegetables have roasted thoroughly. Bring the water to a boil, then turn down to a simmer. An excellent broth made by dry roasting is ginger root and carrot, with chopped parsley sprinkled on top shortly before serving.