How to Make It
Preheat oven to 350°.
Spread walnuts on a rimmed baking sheet and toast in oven for 10-12 minutes (rotating occasionally), or until fragrant. Let cool.
In a food processor, combine ¾ cup walnuts, basil, scallion tops, olive oil, parmesan, parsley, chile, garlic, salt, and pepper. Process until smooth.
Cook according to package instructions for al dente; drain pasta, reserving about 1/2 cup cooking liquid.
In a bowl, combine pasta, pesto, and reserved cooking liquid, 1-2 tablespoons at a time, until pesto coats pasta and enough water has been added to loosen up the noodles. Coarsely chop remaining ¼ cup walnuts. Serve pasta topped with walnuts and additional grated Parmesan, as desired. Serve immediately, or keep in an airtight container in the refrigerator for up to 5 days.