Remove and chop the stems. The stems should be easy to remove. Just give a gentle tug and they should pop out.

Cook the chopped stems. Saute the chopped stems in olive oil until the mushrooms have released their moisture. Keep cooking until the pan is almost dry.
Add the remaining stuffing ingredients.

Fill the mushroom caps with the stuffing. I like to use a small spoon. Definitely tamp down on the stuffing but don’t pack it too tightly! Go ahead and mound a bit on the top! Bake them in an oiled casserole dish. This helps hold the mushrooms upright and prevent spillage of that wonderful stuffing.
Ready to serve.