Warm oil and butter in a large skillet over medium-high heat. Add onions and peppers and cook over high heat 4 minutes. Stir in minced garlic, cook 30 seconds. Simmer 5 minutes until cooked through. Remove from heat and season to taste.
Soak bread in water to cover (5 minutes). Squeeze out excess water.
Combine soaked bread, turkey, prosciutto, sausage, eggs, Parmigiano-Reggiano, nutmeg, 1/4 cup Pecorino, 1/4 cup parsley, and 1/4 cup olive oil in a large bowl and mix very gently with your hands.
Season with salt and pepper. Form mixture into 2-inch balls. Place balls on a baking sheet, cover, and refrigerate 1 hour to allow flavors to blend.
Warm remaining 1/4 cup olive oil in a 12 inch heavy-bottomed skillet over high heat until almost smoking. Brown meatballs on all sides. Transfer to a plate and drain oil from pan.
Add spaghetti sauce and wine to the pan and bring to a boil. Place meatballs in sauce and return to a boil, then reduce heat and simmer 30 minutes.
Slice open hero rolls and fill each with 3 meatballs and sauce. Top each with provolone cheese and some peperonata. Transfer sandwiches to a platter and serve with remaining Pecorino and parsley sprinkled over the top.