Preheat your oven to 400°F (200°C).

Grease a medium baking dish with melted butter.

Clean the mushrooms under cold water and remove the stems.

Dip each mushroom cap in the melted butter and arrange them upside down in the prepared baking dish. Sprinkle with salt and bake for 10-15 minutes.

Flip each mushroom cap right-side up and drain excess liquid.

In a mixing bowl, combine cream cheese, Parmesan, mozzarella, bacon, and green bell pepper. Mix well.

Fill each mushroom cap with the cheese mixture, being careful not to overfill.

Sprinkle paprika over the stuffed mushrooms and pour remaining melted butter over the tops.

Return mushrooms to the oven and bake for an additional 20 minutes.

Let cool slightly before serving warm, optionally with marinara sauce.