Preheat oven to 400° and place a wire rack inside of a foil lined baking sheet - Set aside
Remove the stems from your mushrooms and clean the caps with a damp paper towel to remove any debris
Toss or brush mushrooms with the olive oil and season with ½ tsp of salt - Arrange cap side up/stem side down on the wire rack and place in the oven - Allow to bake for 10 minutes releasing their liquid into the baking sheet - remove from oven and set aside until cool enough handle (DO NOT TURN OFF OVEN)
In a small bowl, stir together the breadcrumbs and melted butter – Set aside until needed
In a medium bowl, mix the cream cheese until smooth - Mix in the parmesan, about ¾ of the chives, parsley, garlic, mayonnaise, mustard, Chesapeake Bay Seasoning, lemon juice, lemon zest, pepper, and remaining ⅛ tsp salt until thoroughly combined - Gently fold in the crab meat
Fill the mushroom caps with the crab meat filling (2-3 Tablespoons each for the cremini/baby bella OR ¼ of the mixture each for the full sized portobellos) and return to the wire rack - Top each with the breadcrumb butter mixture - Return to the oven
Allow to bake until the breadcrumbs are browned, and the filling is hot and melty (apx 15-20 minutes)
Garnish with the remaining chives and serve as hors d’ouvres (cremini/baby bella) or as a main