clean mushrooms and remove stems
brown the ground beef, cut up stems and add to a fry pan along with the onion and ham
add remaining ingredients and simmer until until cooked.
Place mushrooms onto a cookie tray (optional: line tray with parchment paper or silicone map to make cleanup easy)
stuff mixture into the mushroom caps. sprinkle with grated mozza and parmesan
place tray of mushrooms under the broiler for about 5 minutes