In a nonstick skillet, heat the olive oil over medium-high heat until hot. Add the mushrooms and sauté, stirring constantly, until they have given up their liquid and it evaporates, and the mushrooms have begun to caramelize, about five minutes. Stir in the onion, celery, garlic and parsley, reduce the heat and continue to cook until the vegetables have softened slightly, five to seven minutes. Remove from heat and set aside to cool. Meanwhile, heat the oven to 375 degrees.

In a large bowl, combine the ground pork and beef with the cooled vegetable mixture, fennel, red pepper, mushroom powder, breadcrumbs, egg and salt, mixing until thoroughly combined. Set aside 2 cups of the meat mixture to use in the tomato sauce.

Form the remaining mixture into 12 meatballs, each roughly 2 ?½ inches in diameter. Place the meatballs on a parchment-lined baking sheet and bake until the meatballs are browned and cooked through, 15 to 20 minutes.