Wipe the portobello caps clean of any dirt and use a knife to remove the stems.
Combine the crab, egg, mayonnaise, parsley, bell pepper, onion, seasonings, and 2 tablespoons almond flour in a large bowl. Gently mix until well combined.
Place the mushrooms in a baking dish and stuff with the crab mixture. Sprinkle a small pinch of almond flour on top of each mushroom, then drizzle the olive oil over them.
Bake for 25-30 minutes, until the tops are golden brown and the mushrooms are tender.