Preheat the oven to 400°F. Cut the bread into 10 pieces. Place the bread in a large bowl. Pour 4cups of warm water over the bread. Using your hand, push the bread to the bottom of the bowl so that it will soften as it absorbs the warm water. Set aside for 5 minutes. Drain the bread in a colander. Squeeze out as much water as you can, pushing down on the bread. Turn the drained bread into a large bowl.
Cut ¼inch off the top of each pepper. Mince the top pieces (discard the stems) and add them to the bread. Cut each pepper in half. Remove and discard the seeds and soft ribs from each pepper half. Set aside. Add the garlic, parsley, zucchini, mushrooms and onion to the bread. Toss well to mix. Drizzle the olive oil over the bread mixture. Add the oregano, salt, and pepper to taste. Add the eggs. Toss well to combine.
Divide the filling among the pepper halves, mounding as necessary. Place the pepper halves in a large roasting pan. Pour the hot water around (not over) the peppers. Cover tightly with foil. Bake for 45-60 minutes until the peppers are fork-tender.