This comes from Cook’s Country, December/January 2007, with a few modifications, as usual. Sometimes I have found some perfect stuffing-sized mushrooms at Safeway.
Heat oven to 450 degrees. Set a wire rack inside a baking sheet. Toss mushrooms with oil, lemon juice, 1/4 tsp. salt, and 1/8 tsp. pepper. Arrange mushrooms, gill side up, on rack and roast about 20 minutes. Turn caps over and roast about 10 more minutes.
Cool mushrooms. Process all ingredients except the last four listed in food processor until smooth for the filling.
Fill mushrooms. I use a spoon for this. You can refrigerate them at this point on a paper towel-lined plate.
Mix together bread crumbs, parsley, garlic, and olive oil. Just before serving, press each cap into the topping mixture and bake until hot and slightly browned. Maybe 10 minutes or so.