Preheat your oven to 350ºF (175ºC). Arrange the bread slices and raw walnuts on a baking sheet in a single layer. Toast for 8–10 minutes until the bread is lightly browned and the walnuts smell toasty.

Bring about 4 quarts of water to a rolling boil in a large pot. Salt generously and add your pasta. Cook for 2 minutes longer than package instructions for al dente, then reserve 1 cup pasta water before draining.

In a food processor combine toasted bread, toasted walnuts, drained roasted red peppers, roughly chopped garlic, lemon juice, smoked paprika, red pepper flakes, kosher salt, and cracked black pepper. Pulse until thick paste, then stream in olive oil while processing until smooth.

In a small bowl, combine reserved fresh breadcrumbs with lemon zest, parsley, basil, capers, and a pinch of flaky salt.

In a large serving bowl, mix the cooked pasta with the roasted red pepper sauce, adding reserved pasta water to adjust consistency. Fold in chopped arugula and optional herbs or capers.

Sprinkle the herby breadcrumb mixture over the pasta and finish with a drizzle of olive oil. Serve at room temperature or chilled.