Preparation

• Bring a pot of generously salted water to a boil. Heat the olive oil in a 12-inch skillet over medium-high heat. Cook the chorizo, stirring occasionally, until browned, 2 to 3 minutes. Add the shrimp and cook, stirring occasionally, until it curls up and just begins to turn pink, about 2 minutes; don’t cook it through. Off the heat, use a slotted spoon to transfer the chorizo and shrimp to a bowl.
• Pour off all but 2 Tbs. of the fat from the skillet (or add more oil so you have 2 Tbs. fat in the pan) and set the skillet over medium heat. Add the onion and garlic and cook until softened, about 3 minutes. Stir in the tomatoes with their juices and the pepper flakes, scraping the bottom of the pan, and simmer briskly for 5 minutes to blend the flavors.
• Meanwhile, cook the linguine in the boiling water until barely al dente, 4 to 6 minutes. Reserve 1/2 cup of the pasta water and drain the pasta in a colander.
• Add the shrimp and chorizo to the sauce and simmer until the shrimp is just cooked through, another 1 to 2 minutes. Season the sauce to taste with salt. Toss the pasta, sauce, and parsley in the pasta pot over medium-low heat for 2 minutes. The sauce should just coat the pasta; add some of the pasta water to moisten if necessary. Drizzle each serving with a little oil.