Slit an x in the bottom of the Mushrooms then Boil the mushroom for 10 minutes, (sometimes I saute the mushrooms, Onion, Pepper - or keep the onion/pepper uncooked). Place the Mushrooms, Onion, Pepper, Garlic in a glass jar (I like to recycle old tomato sauce jars (if you use them-we all cheat with sauce sometimes), Just make sure you use only glass.
In a pan, add the Oil, Vinegar, and the sugar. Stir and simmer for around 15 minutes.
Cool the marinate, to to jar, make sure you cover all the mushroom, and herbs.
Place in frig for 24 hours (or longer), THEN EAT -- MMMM -- OR you can can this if you know how.