Preheat oven to 375 degrees. Butter a 9x13-inch baking dish, set aside.
Wash and dry mushrooms. Remove stems; chop and reserve for stuffing. Fry diced bacon in skillet. Drain and reserve 2 Tablespoons drippings. Saute onion, green pepper, and mushroom stems in bacon drippings. Add bacon, salt and pepper. Cool slightly and combine with cream cheese.
Press mixture firmly into mushroom caps, mounding slightly. Top with buttered bread crumbs. Place mushrooms in buttered baking dish. At this point, mushrooms may be covered and refrigerated 1 to 2 days. Add hot water to baking dish and bake uncovered 15 to 20 minutes. Garnish each with parsley, if desired.