Combine the 2/3 cup of olive oil, 1/2 cup of water, juice of 2 lemons, bay leaf, bruised garlic cloves, peppercorns and salt in a 10 to 12 inch enameled or stainless steel skillet, and bring to a boil over moderate heat. Reduce the heat, cover and simmer for 15 minutes.
Strain this marinade through a sieve and return it to the skillet; bring to a simmer over low heat.
Drop the mushrooms into the marinade and simmer, turning them over from time to time, for 5 minutes. Let the mushrooms cool in the marinade.
Serve marinated mushrooms at room temperature or, after the marinated mushrooms have cooled, refrigerate mushrooms and serve mushrooms cold.
Marinated mushrooms will keep in the refrigerator at least two days. Before serving, lift the mushrooms out of the marinade with a slotted spoon, draining them carefully, and arrange mushrooms on a platter or in a serving bowl. Serve as part of an antipasto.