Place cleaned mushrooms in serving bowl (one that can handle boiling liquid) and set aside. In a sauce pan mix oil, lemon juice, water, garlic, salt, and pepper. Bring mixture to a boil. Stir in a pinch of red pepper flakes if using. Pour over mushrooms. Cover dish and refrigerate for at least 2 hours, preferably overnight. Just before serving add parsley and peppers if using.
These keep in refrigerator like pickles.