Preheat oven to 375 degrees. Remove and discard stems from the mushrooms. Wipe the mushroom caps clean with wet paper towels.
Place the crabmeat in a small bowl. With a fork, break up the pieces slightly until they are flaky. Add the mayo, lemon, thyme, red pepper, garlic and scallions and combine.
Fill each mushroom cap with the crab mixture. Place on a baking sheet lined with parchment paper or aluminum foil.
Bake for 15-17 minutes, until slightly browned and bubbly. Allow to cool for 2-3 minutes, then transfer to a serving dish and sprinkle with fresh parsley.