Clean the portobello mushrooms by wiping them with damp paper towel, remove stems, and finely chop them.

Preheat a saucepan, sauté onion and garlic until soft. Add chopped mushroom stems and cook for 3-4 minutes.

Transfer sautéed mixture to a bowl, add walnuts, sun-dried tomatoes, parsley, salt, and pepper. Combine thoroughly.

Stuff each mushroom cap with the mixture and place on a baking sheet.

Preheat oven to 350º F, bake stuffed mushrooms for 15 minutes until golden brown.

Mix chopped parsley in a separate bowl for dressing.

Serve the baked stuffed mushrooms with the parsley dressing for a flavorful dish.