Place bread into a large bowl. Pour water over the bread; add egg. Press mixture down with fists, turning as needed, until bread is evenly moistened and crumbled.
Melt lard in a large skillet over medium heat. Add onions and parsley; simmer until onions are tender, about 10 minutes. Reduce heat to low. Stir in vinegar, red pepper flakes, salt, and ground black pepper; simmer until flavors combine, about 5 minutes.
Pour onion mixture over the bread mixture, turning the bread while pouring; mix until stuffing mixture is evenly combined.
Preheat oven to 325 degrees F (165 degrees C). Spray 2 baking sheets with nonstick cooking spray.
Form stuffing mixture into 3-inch balls; place onto baking sheets 1 1/2-inches apart.
Bake in the preheated oven until golden brown, 18 to 20 minutes.