Preheat the oven to 300 degrees F.

Place cubed stale Italian bread on a baking sheet and bake for 10 minutes to dry.

Cool the bread and pulse in a food processor until fine crumbs form.

Bring a large pot of salted water to a boil.

Add bucatini pasta and cook until al dente, reserving 1 cup of cooking water.

Drain the pasta.

In a large saute pan, heat 4 tablespoons of olive oil over medium-high heat.

Add bread crumbs and cook until golden and well coated, then remove from pan.

Add the remaining 4 tablespoons of olive oil to the pan.

Add minced anchovy fillets and minced roasted red bell peppers and cook rapidly for 2 minutes, stirring.

Add finely minced sweet onion and cook for 6 to 8 minutes, stirring frequently.

Add thinly sliced garlic and red chili flakes, and cook for 3 to 4 minutes.

Add 1/2 to 1 cup of the bread crumbs and half of the grated Parmigiano-Reggiano cheese.

Stir in the cooked bucatini pasta, tossing to combine, and adding reserved cooking liquid as needed to create a sauce.

Transfer to a serving platter.

Garnish with remaining cheese, bread crumbs, and minced Italian parsley leaves.

Serve immediately.