Wipe the mushroom caps clean using a damp paper towel to remove any dirt. Gently remove the stems and reserve the caps. Finely chop the mushroom stems and set them aside for the filling.

In a skillet over medium heat, warm 1 tablespoon of olive oil. Add the chopped mushroom stems and cook for 3 to 4 minutes, stirring occasionally, until they soften. Stir in the chopped spinach, minced garlic, and chopped marinated artichokes. Continue sautéing for an additional 2 to 3 minutes, until the spinach has wilted and everything is evenly combined. Remove the pan from the heat and allow the mixture to cool slightly.

In a mixing bowl, add the softened cream cheese, chopped walnuts, parsley, thyme, salt, and black pepper. Add the cooled mushroom stem, spinach, and artichoke mixture and stir until fully incorporated.

Fill each mushroom cap with the cream cheese mixture, pressing it in gently so the filling is packed. Place the stuffed mushrooms onto the prepared baking sheet.

Top each mushroom with grated Parmesan cheese. Lightly drizzle the mushrooms with olive oil to encourage browning. Bake for 15 to 20 minutes, until the mushrooms are tender and the filling is golden and bubbly.

Remove from the oven and let the mushrooms cool slightly before serving. Garnish with additional fresh parsley or thyme if desired.