Melt margarine in nonstick skillet; add scallion and saute for 2 minutes.
Add mushrooms, salt, pepper, and thyme and cook 3 to 5 minutes or until all liquid has evaporated; cool.
Cut each egg in half lengthwise; remove yolks and reserve whites.
Push yolks through a sieve into a bowl.
Add mushroom mixture, mayonnaise, and lemon juice; stir to combine.
Fill each egg white with an equal amount of mixture and garnish with a parsley sprig.