Heat butter in a 1-quart souffle dish, uncovered, at 100% power for 2 minutes, until melted. Add mushrooms and stir to coat. Cook, uncovered, at 100% power for 5 minutes.

Put shallots and parsley in the workbowl of a food processor and process until finely chopped. Remove mushrooms from oven. Stir in shallots, parsley, salt and pepper. Cook, uncovered, at 100% power for 8 minutes. Remove from oven.