Step 1

Place the bread cubes in a food processor and process until finely ground. In a large skillet, heat ⅓ cup of olive oil over medium heat. When hot, add in breadcrumbs and cook until golden in color, about 3 minutes, stirring to make sure they don't burn. Remove breadcrumbs from skillet and set aside.

Step 2

Bring a large pot of salted water to boil. Boil spaghetti until just al dente, according to package instructions. Save a cup of the cooking liquid for the sauce. Drain spaghetti and set aside.

Step 3

While the pasta boils, prepare the sauce. In the large skillet, heat the remaining ⅓ cup of olive oil over medium heat. Add the garlic, anchovies, and chili flakes. Cook until fragrant and the anchovies dissolve; about 3 minutes. Add in one cup of pasta water, lemon juice and zest, and bring mixture to a simmer. Cook until sauce has reduced slightly; about 4 minutes.

Step 4

To the saucepan add in the cooked spaghetti, chopped parsley, parmesan cheese, and breadcrumbs. Toss until well combined. Serve immediately.