In a large pot, add water (just need enough water that will cover the mushrooms) and the lemon juice. Bring to a boil.
While you bring the lemon water to a boil, clean and wash mushrooms.
Trim off the stems. If you have some larger mushrooms like I did, cut the larger ones in half (the mushrooms do shrink when you boil them in the water, so don’t cut the smaller ones)put them in a large pot.
When the lemon water has come to a boil, carefully add the mushrooms. Let them boil for about 5 minutes (you don’t want to boil them until they’re super soft, just a quick boil).
While the mushrooms are doing their quick boil, bring the marinate to a boil.
In a small pot, add the olive oil, vinegar, garlic cloves, salt, oregano, dried parsley, and crushed red pepper flakes. Bring to a boil and let boil for about 3 minutes (should be about same time as it takes to boil the mushrooms, it’s ok if it goes over a minute or two). When it’s boiled for a few minutes, remove from heat so you can deal with the mushrooms.
Remove the garlic cloves from the olive oil marinate and reserve in a small plate.
Drain the mushrooms in a colander. Spoon them into your canning jars (or whatever container you are storing them in)add a garlic clove to each jar, and leave about 1/2 inch of headspace on the top.
When you have your mushrooms ready in the jars, stir the marinade together and carefully pour the olive oil marinade over the mushrooms in the jars, being sure to leave that 1/2 inch of headspace on the top.
Cover, using lids and store them in the refrigerator. They can be stored in the refrigerator up to two weeks.
Serve at room temperature.
Use the marinated mushrooms in salads, antipasto, pasta salad, or just enjoy straight from the jar.