Gather all ingredients. Wipe the mushrooms clean with a dry paper towel. Unless the mushrooms are very small, cut then down into small, bite-sized pieces of approximately the same size. I suggest either quartering them or cutting them into 1/6.
Combine the water, vinegar and salt in a large saucepan over medium-high heat and bring it to a boil, while whisking to dissolve the salt.
Add the mushrooms, chilis, shallots, thyme and garlic to the boiling water and stir until well-combined. Push the mushrooms down to ensure they are immersed in the liquid as best as possible. Cover the pot and cook until the mushrooms are tender, but not overcooked. This should take about 6 to 8 minutes. Stir occasionally.
Once the mushrooms are soft, remove the pot from the heat and let the mixture cool a bit. Once cooled, remove and discard all thyme springs, then transfer the entire mixture (including the liquid) to a glass vessel and store it in the refrigerator, covered, for at least 2 hours and up to 2 weeks.
When ready to serve the mushrooms, remove them from the vinegar solution with a slotted spoon and transfer them to a bowl. Drizzle them with extra-virgin olive oil, toss with parsley and serve. That’s it! Buon Appetito!