0.75 cup natural green olives (not brined but packed in water)
0.75 cup walnuts
2 teaspoons coconut vinegar OR white vinegar
1 teaspoon thyme leaves
Preheat the oven to 350 degrees.
Use a damp towel to wipe off any dirt from the mushrooms. Remove the mushroom stems and add them to a food processor fitted with the S blade. Add in the onions and garlic. Pulse to finely chop the mixture.
Over medium heat, heat the oil in a skillet. Once the oil is warm, add in the mushroom stems, onion, and garlic mixture. Stir in the salt and pepper. Saute until the mushrooms have released their moisture and the mixture is softened, about 10 minutes. Remove from the heat and transfer to a bowl.
Add the walnuts, olives, coconut vinegar, and thyme leaves into the food processor. Pulse until the mixture is finely chopped. Add this to the bowl and stir to combine.
Line up the mushrooms, stem side up, on a baking tray lined with nonstick foil. Fill each mushroom cap with some of the filling. Bake for 35-45 minutes. Drizzle with balsamic reduction and serve.