Make the chimichurri: Pulse parsley, garlic, oregano, red pepper flakes, olive oil, and red wine vinegar in a food processor until finely chopped. Season with salt and pepper.
Cook the pasta: Boil pasta in salted water until al dente. Reserve 1 cup of pasta water, then drain.
Season the shrimp: Pat shrimp dry, then toss with olive oil, salt, and black pepper.
Cook the shrimp: Sear shrimp in a hot skillet for about 2 minutes per side, or until pink and opaque. Transfer to a plate.
Toss everything together: Add pasta and chimichurri to the skillet over low heat. Toss gently, adding reserved pasta water as needed.
Garnish and serve: Return shrimp to the pasta, toss once more, then finish with parsley, lemon, Parmesan, or red pepper flakes if desired. Serve immediately.
