Tear the bread into chunks and pulse in a food processor until you have coarse, pea-sized crumbs, about 80 g.

Heat 3 tbsp olive oil in a 30 cm / 12-inch skillet over medium heat. Add the breadcrumbs and a pinch of salt, toast for 4 to 5 minutes, stirring often, until deep golden and crisp.

Watch closely in the last minute, the crumbs turn from golden to burnt fast once the oil is hot. Transfer to a bowl and wipe out the skillet.

Bring a 6-quart / 5.7 L pot of water to a boil and salt it generously.

In the same skillet, warm the remaining 3 tbsp olive oil over medium-low heat. Add the garlic and chili flakes, cook for 2 to 3 minutes until the garlic turns pale gold. Don't let it brown or it turns bitter.

Cook the pici in the boiling water until al dente, 3 to 4 minutes for fresh or per package directions for dried. Reserve 1 cup of pasta water, then drain.

Add the drained pici to the skillet with the garlic oil. Toss over low heat with a splash of the reserved pasta water until the strands are glossy and coated, 1 to 2 minutes.

Remove from heat and stir in the parsley and lemon zest, if using.

Divide among bowls, top generously with the toasted breadcrumbs, and finish with black pepper. Serve right away while the crumbs are still crisp.