Preheat oven to 350, and set out cream cheese to soften.
Clean mushrooms and pull out the stems. Line up mushrooms in a glass pan.
Slice off the tip of the stem and discard. Chop remaining of the stem and the onion and cook in a skillet with oil until very soft; approx. 15 min.
Move onion and mushroom mixture to a mixing bowl. Add in Garlic, Breadcrumbs, Crab, and seasonings and stir together.
Add in the cream cheese and mix well.
Using a teaspoon fill each mushroom to a rounded top. Your mushrooms will appear overfilled.
Top each mushroom with mozzarella.
Place butter in the pan to keep mushrooms from sticking and for added flavor.
Cover with foil and bake 20 min. Remove foil and cook 5 min longer until cheese is golden.
Optional, squeeze fresh lemon juice over each mushroom.