Preheat the oven to 375 degrees F (190 degrees C). Brush a large baking sheet with about 1/4 cup of melted butter. Arrange mushroom caps in a single layer over the baking sheet.
In a medium bowl, mix together the crushed croutons, remaining 1/2 cup butter, shredded cheese, crabmeat, lobster and garlic. Spoon into mushroom caps where the stems used to be.
Bake for 10 to 12 minutes in the preheated oven, or until lightly browned on the top. Sprinkle with additional cheese if desired, and serve hot!
