Preheat your oven to 350 degrees F. Spread the bread cubes in an even layer on an ungreased baking sheet. Bake until the cubes are lightly toasted, about 12 minutes, stirring twice during the baking to ensure they toast evenly. Let the cubes cool, then place them a very large mixing bowl. Increase the oven’s temperature to 375 degrees F. Lightly coat a 9x13-inch dish with baking spray and set aside.
Heat 1 tablespoon olive oil in a large, deep skillet over medium. Saute the mushrooms until browned and they have given up their juices, about 8 minutes. Remove from the pan and set aside.
Return the skillet to the heat, then add the remaining tablespoon olive oil. Once the oil is hot, add the bacon pieces and cook, stirring occasionally, until golden brown and crisp, 7-10 minutes. With a slotted spoon, transfer the pieces to a paper towel-lined plate.
Discard all but 2 tablespoons of the bacon fat from the skillet. Increase the heat to medium high, then add the onion, celery, salt, and pepper and cook, stirring occasionally, until brown and soft, about 5 minutes. Add 3 cups of the chicken stock and bring to a simmer. Once the stock is hot, pour the skillet contents over the bread cubes.
Let the bread mixture cool for a few minutes until it is no longer hot, then add the mushrooms, prunes, beaten eggs, parsley, and rosemary. The mixture should be very wet, so add additional chicken stock as needed.
Transfer the stuffing to a prepared baking dish. Coat a large piece of aluminum foil with cooking spray, then use it to cover the stuffing, spray side down. Bake the stuffing for 20 minutes, remove the foil, then bake for an additional 30-40 minutes, until the top is golden brown and fairly dry. Let cool 10 minutes, then enjoy.