Portobello mushrooms are a wonderful main dish, due to their heartiness, meatiness and size. Originally published in the Vegan Table cookbook and again in Vegan's Daily Companion by Colleen Patrick Goudreau.
Remove stems from mushrooms, and lightly wipe tops with a damp paper towel.
In a large bowl, combine vinegar, soy sauce, water, rosemary, thyme and oregano. Stir to mix. Add mushrooms and make sure each one is covered by marinade. You may need to move them around. Marinate for as little as 30 minutes or up to overnight in the fridge.
When ready to cook, add some of the oil to a large skillet over medium heat. Remove mushrooms from marinade(but do not discard marinade). Put as many mushrooms as you can fit in pan, tops down. They will shrink as they cook. Cook 3-5 minutes, until lightly browned. Turn over and cook 3-5 minutes more.
Remove fresh herb sprigs from marinade, and pour marinade into pan, reserving some for additional batches of mushrooms.
Cover and cook 5-7 minutes. Flip mushrooms, cover and cook 5-7 minutes longer. When fork tender, remove from pan, and repeat with remaining nmushrooms.
To serve the mushrooms hot, simply use myltiple pans on the stove at once.