Line a quarter-sized cookie sheet with foil and rub the foil with 1 tbsp of olive oil.
Wash mushrooms, and snap off stems. Wash by gently rinsing and rubbing off dirt with fingers. Do not submerge and quickly blot dry.
Snap off the stems and place on a cutting board. Place the de-stemmed mushroom cap on a foil-lined pan. I used a quarter-sized cookie sheet.
Chop the parsley, onion, garlic and mushroom stems into tiny pieces.
Make Herbed Stuffing
Mix the breadcrumbs (or alternative), onions, parsley, garlic and stems in a bowl. Drizzle in olive oil and keep mixing until the mixture is sticky so that when you compress 2 tbsp, it sticks together. I used about 3 tbsp in the crumb mixture, and the other tbsp on the pan.
At this point, you really should taste-test for enough salt, Italian seasoning, nutritional yeast flavor, etc. Adjust by adding spices as you wish.
Press the mixture into each mushroom that lines your pan. Drizzle the mushrooms again with olive oil, about 1 tbsp or spray tops with olive oil spray.
Bake at 375 F for 30 minutes or until the top is golden and crunchy. Don't go beyond 45 minutes or they will dry out.
Store Stuffed Mushrooms.
I let them cool, then put them covered in the refrigerator. They last at least 4 days maybe a bit longer. Do not freeze them or they will be too soggy once thawed.