Pistachio Pesto Pasta

0 Cook the Pasta: Bring a large pot of water to a boil. Once boiling, add the rigatoni and salt; stir well. Reduce the heat to medium and simmer the pasta until it has reached an al dente texture (check the package instructions for cook time). Drain the pasta, but do not rinse.
1 Pistachio Breadcrumbs: While the water is coming to a boil, add 1/4 cup of pistachios to a food processor with an S-blade attachment. Pulse the  pistachios until they are finely chopped, resembling the same size and texture as breadcrumbs. Remove from the food processor and set aside.
2 Pistachio Pesto: Return the empty food processor to its base and add the remaining 1/4 cup pistachios, garlic, lemon juice, and red chili flakes if using. Pulse until the pistachios and garlic are finely chopped, scraping the sides of the food processor with a spatula as necessary. Add the basil and parmesan to the food processor and pulse again until chopped. Close the food processor and turn it on, slowly drizzling the olive oil into the basil mixture through the opening in the top. Process until the basil is finely chopped and the mixture is mostly smooth but with some texture, scraping down the food processor as necessary. If the pesto is too thick for your liking, add additional olive oil in 1 tablespoon increments. Set aside.
3 Cook the Breadcrumbs: Warm the olive oil in a medium saucepan over medium heat. Add the garlic and sauté for 45 to 60 seconds, until the garlic is fragrant but before it starts to brown. Add the panko breadcrumbs to the oil and mix well. Sauté for 2 to 3 minutes, stirring frequently, until the breadcrumbs are beginning to turn golden. Add the chopped pistachios from step 2 and toast for an additional 1 to 2 minutes, until the breadcrumbs are fully golden. Remove the pan from the heat and immediately transfer the breadcrumbs to a small plate or bowl so they do not burn. Set aside.
4 Combine: Return the pasta to the pot (or the breadcrumb pan) and add all of the pesto. Mix well, until all of the pasta is evenly coated in pesto. Add any salt or red pepper flakes to taste, if necessary.
5 Serve: Divide the pasta between serving bowls and top with a generous amount of pistachio breadcrumbs. Serve warm; store any breadcrumb and pasta leftovers in separate containers in the refrigerator for up to 3 days.