Preparation

In a food processor, combine the arugula, pistachios, Parmigiano, and garlic, and pulse until finely ground, about 1 minute. With the motor running, add 3/4 cup of the oil in a slow, steady stream until the pesto is smooth, about 1 minute. Transfer the pesto to a small bowl, stir in the salt, and set aside.

In a large Dutch oven, heat the remaining 2 Tbs. oil over medium heat. Add the onion, and cook until softened, about 3 minutes. Add the pasta and broth, and bring to a boil. Cook, uncovered, stirring constantly, until the pasta is al dente and the liquid is absorbed, 8 to 10 minutes. Reduce the heat to low, add the asparagus and pesto, stir to combine, and cook until tender, about 2 minutes. Remove from the heat. Add lemon zest and juice, and stir to combine.

Divide among pasta bowls, garnish with the lemon wedges and pepper flakes, and serve immediately.