Warm olive oil and butter in a large skillet over medium-high heat.

Add diced red onions, red bell peppers, and yellow bell peppers to the skillet.

Cook the vegetables over high heat for 4 minutes.

Stir in minced garlic and cook for 30 seconds.

Simmer for 5 minutes until the vegetables are cooked through.

Remove from heat and season the vegetable mixture to taste with salt and pepper.

Soak cubed day-old bread in water to cover for 5 minutes.

Squeeze out the excess water from the soaked bread.

In a large bowl, combine the soaked bread, ground turkey, diced prosciutto, Italian sausage, lightly beaten eggs, grated Parmigiano-Reggiano cheese, freshly grated nutmeg, 1/4 cup grated Pecorino Romano cheese, 1/4 cup minced Italian parsley, and 1/4 cup olive oil.

Mix the ingredients gently with your hands.

Season the mixture with salt and pepper to taste.

Form the mixture into 2-inch balls.

Place the meatballs on a baking sheet, cover, and refrigerate for 1 hour to allow flavors to blend.

Warm the remaining 1/4 cup olive oil in a 12-inch heavy-bottomed skillet over high heat until almost smoking.

Brown the meatballs on all sides.

Transfer the browned meatballs to a plate and drain the oil from the pan.

Add non-meat spaghetti sauce and dry white wine to the pan and bring to a boil.

Place the meatballs in the sauce, return to a boil, then reduce heat and simmer for 30 minutes.

Slice open hoagie rolls and fill each with 3 meatballs and sauce.

Top each sub with provolone cheese and some peperonata (cooked pepper mixture).

Transfer the sandwiches to a platter and serve with remaining Pecorino cheese and parsley sprinkled over the top.