From Whole Foods
URL: http://www.wholefoodsmarket.com/recipes/recipe.php?recipeId=66

Serves 4 as an appetizer

A reader sent us this recipe that she's been making for over 40 years. We replaced the dried herbs with fresh oregano and parsley and added some garlic and onion to boost the flavor even more. These mushrooms make a great addition to an antipasti platter with cubes of cheese, a pile of olives, slivers of roasted red peppers and paper-thin slices of prosciutto.

Ingredients

1 pound fresh cremini mushrooms
2 tablespoons extra virgin olive oil
2 to 4 tablespoons white wine vinegar, or to taste
1 to 2 cloves minced garlic (optional)
1/4 cup minced red onion
2 teaspoons fresh minced oregano
2 tablespoons fresh minced Italian parsley
Sea salt, to taste
1/2 teaspoon each black peppercorns and coriander seeds

Method

Clean mushrooms and remove stems. Simmer mushroom caps in salted water for 5 minutes or until mushrooms are tender. Drain and transfer to a bowl. Add olive oil, vinegar, garlic, red onion, oregano, parsley, salt, peppercorns and coriander. Stir to combine. Taste and adjust seasoning. Marinate in the refrigerator for several hours or overnight. Bring to room temperature before serving.
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From Cooks.com
URL: http://www.cooks.com/rec/view/0,1758,128189-249199,00.html

MARINATED MUSHROOMS	 

1/3 cup red wine vinegar
1/3 cup extra virgin olive oil
1 lb. mushrooms
5 cloves garlic
1 teaspoon salt
1/2 teaspoon oregano, minced
1/2 teaspoon basil, minced
1 large shallot, minced
2 green onions, chopped
1/4 teaspoon hot red pepper flakes
finely chopped red or green sweet peppers (optional)

Note: Use fresh herbs when available. If using fresh basil and oregano double quantities.

Brush off fresh mushrooms to clean.

Bring all other ingredients to a boil in a medium saucepan. Reduce heat and simmer (small bubbles) for 6 minutes. Toss in mushrooms and stir; cover pan. After 1 more minute of cooking, remove pan from heat, uncover and allow to cool.

Pour into clean jar and store in refrigerator. Serve cold. Great for bringing as a side for picnics.

Quantities may be doubled for a larger batch. Keeps up to 1 month in refrigerator.

If you like an extra tangy version, add 1 tablespoon of lemon juice or balsamic vinegar.