Servings: 24 Preheat oven to 425. In a food processor bowl or blender container, Place the oil, chopped nuts, basil, parmesan cheese, and garlic. Process or blend until smooth. Add pepper to taste. Remove and discard stems from mushrooms. Clean mushrooms. Spoon a rounded teaspoon of pesto into each mushroom cap. Place a walnut half or several pine nuts atop each. Bake for about 10 minutes or until hot. Drain on a paper towel. Serve warm..