Clean mushrooms. Seperate stems form caps. Finely chop steams, onion and garlic. (I used my food processor.)
Melt butter in a pan then add everything except the mushroom caps and the mozzarella cheese. Cook untill onion and mushrooms are tender.
Spray bottom of pan with nonstick spray. Place mushroom caps in pan. Stuff with cracker mixture. Bake at 425 for 5 minutes or untill mushrooms are tender. Top with mozzarella cheese and broil until chesse is melted.