Preheat the oven to 425℉. Spray a small baking dish with nonstick spray.
Lightly rinse the mushrooms and pat dry with paper towels. Pull off the stems and save two. Mince the tender portion of those two mushroom stems and place in a small bowl. Place the mushrooms, removed stem-side-up, in the prepared baking dish.
Add the remaining ingredients to the minced stems in the bowl. Stir to mix well. Divide the mixture between the mushroom caps, using a small spoon, mounding the filling into the center of each mushroom.
Bake 13 to 15 minutes, or until the mushrooms are tender and the filling mixture is hot and sizzling. Let the mushrooms cool slightly before serving.