Mushrooms stuffed with Tomatoes and Olives

Ingredients

 * ⅓ cup chopped walnuts
 * ½ oz sun-dried tomatoes, preferably organic (about 6 pieces)
 * 1 small all-purpose potato, peeled and quartered
 * 3 tbsp skim milk or soy milk
 * 36 small to medium-size mushrooms (about 1 lb), stems removed and reserved
 * 1 tbsp olive oil
 * 1 cup finely chopped onion
 * 4 cloves garlic, minced
 * ⅛ tsp crushed red pepper flakes, or more to taste
 * 2 tbsp grated romano cheese, optional
 * 2 tbsp chopped fresh flat-leaf parsley

Directions

 * 1) Preheat oven to 375°F.
 * 2) Spread walnuts on baking sheet, and toast in oven until lightly browned and fragrant, about 6 minutes. Set aside to cool.
 * 3) Reduce oven temperature to 350°F.
 * 4) Put sun-dried tomatoes into small bowl, and cover with hot water.
 * 5) Cover with plastic wrap, and let stand until tomatoes are plump, about 30 minutes.
 * 6) Drain well, and chop. Set aside.
 * 7) Meanwhile, steam potato quarters until tender, about 15 minutes.
 * 8) Transfer to small bowl, and let cool slightly.
 * 9) Mash potato quarters with fork, then add milk and stir until smooth. Set aside.
 * 10) Finely chop enough mushroom stems to equal ⅓ cup, and set aside.
 * 11) Reserve remaining stems for another use; store them in refrigerator up to 3 days.
 * 12) In large skillet, heat oil over medium heat.
 * 13) Add onion, garlic and red pepper flakes, and cook, stirring often, until onion begins to brown, about 10 minutes.
 * 14) Add sun-dried tomatoes and chopped mushroom stems, and cook, stirring often, scraping bottom of pan occasionally, 2 to 3 minutes.
 * 15) In medium bowl, mix all ingredients except mushroom caps.
 * 16) Mixture should be moist but hold its shape well.
 * 17) Add small amounts of water if mixture is too dry.
 * 18) Season with salt to taste (filling can be made ahead and refrigerated up to 2 days. Return to room temperature, and moisten with additional water if necessary before proceeding).
 * 19) Coat shallow baking dish with nonstick cooking spray.
 * 20) Spoon filling into mushroom caps, mounding slightly.
 * 21) Arrange mushrooms in prepared baking dish (mushrooms can be prepared up to this point and refrigerated, covered, for 1 day).
 * 22) Bake until mushrooms are tender when pierced with fork and filling is heated through, about 20 minutes.
 * 23) Serve warm or at room temperature.