Preheat your oven to 350°F. Tear the sourdough bread into bite-sized pieces (removing crusts as specified), then spread both the bread and walnuts on a baking sheet. Toast for 8-10 minutes, stirring halfway through, until the bread is golden and crispy and the walnuts are fragrant. This toasting step is crucial—it concentrates the flavors and creates textural contrast in the final salad.

Bring a large pot of salted water to a boil and add the fusilli pasta. Cook for 2 minutes longer than the package directions call for—this extra time ensures the pasta is tender enough to absorb the sauce without becoming mushy. Reserve 1 cup of the starchy pasta water before draining, then rinse the cooked pasta with cold water to stop the cooking process and prevent it from sticking together.

Once the toasted bread and walnuts from Step 1 have cooled slightly, pulse half of the bread crumbs in a food processor until finely ground, then set aside. Add the remaining bread crumbs to the processor along with the walnuts, roasted red peppers, garlic, lemon juice, tomato paste, smoked paprika, red pepper flakes, kosher salt, and black pepper. Pulse until a thick paste forms. With the processor running, slowly drizzle in the olive oil until the mixture becomes smooth and creamy—this creates an emulsified sauce that coats the pasta beautifully. I like to add the oil slowly because rushing it can make the sauce break and become grainy.

While the sauce is being made, toss the reserved bread crumbs from Step 3 with the lemon zest, fresh parsley, hand-torn basil, chopped capers, nutritional yeast, additional red pepper flakes, and flaky sea salt. This mixture will add brightness, texture, and a finishing touch of umami to the salad. Set aside until ready to serve.

In a large bowl, combine the cold cooked pasta from Step 2 with the red pepper sauce from Step 3. Toss gently, adding pasta water a little at a time until the pasta is evenly coated but not swimming in sauce—you may not need all of the reserved cup. Fold in the baby arugula just before serving; this keeps it fresh and prevents it from wilting. Top with the herb and bread crumb topping from Step 4. I recommend tossing the arugula in just before serving rather than mixing it in earlier, as it stays brighter and maintains its peppery bite.