Remove the mushroom stems from the base and discard. Use a wet paper towel to gently clean the mushrooms.
Preheat oven to 400° F.
In a non-stick skillet, sauté the onion and garlic in the olive oil just until the onions are translucent. Allow the mixture to cool while you prepare the stuffing.
Mix the cream cheese, mayonnaise, and sour cream together. Make sure to fully distribute the cream cheese by pressing the flat part of a silicon spatula down into the mixture to spread the lumps.
Add parsley, basil, chives, red pepper flakes (optional), 1/4 cup of parmesan, and Mrs. Dash. Stir to distribute well.
Add shrimp, mozzarella, and the cooled sautéed onions and garlic and stir. Sprinkle with salt to taste.
Stuff the mushrooms using a cookie dough scoop or a teaspoon. Add 1/2 a teaspoon at a time so that you can fill the cavity of the mushroom cap with stuffing before adding more on top. Use enough stuffing to create a little height, but don’t overdo or the top will fall over during backing. Make the tops relatively flat so they will hold the crumb topping.
Place on a large baking sheet with sides, evenly spaced.
Melt the butter and mix with the remaining parmesan and the panko crumbs. Stir and toss until the entire mixture is even and crumbly. Drop approximately half a teaspoon of the crumb mixture on top of each mushroom. Don’t worry if some falls onto the pan.
Bake for 30 minutes or until the mushrooms are cooked and the tops are a beautiful golden brown.
Cool for 10 minutes or so, then serve warm.