Step 1: Cook the pasta according to package directions in a large pot of salted boiling water until al dente. Before draining, reserve 1 cup of pasta water.
Step 2: While the pasta cooks, pat the shrimp dry with paper towels. Season lightly with salt and pepper.
Step 3: Heat 2 tablespoons of olive oil in a large skillet or pan over medium-high heat. Add the shrimp in a single layer and cook for 1-2 minutes per side, until pink and opaque. Do not overcrowd the pan; cook in batches if necessary. Remove shrimp from the pan and set aside.
Step 4: Reduce heat to medium. Add the remaining 1 tablespoon of olive oil (and optional butter, if using) to the same skillet. Add the minced garlic and red pepper flakes. Sauté for 30-60 seconds until fragrant, being careful not to burn the garlic.
Step 5: Pour in the white wine or chicken broth and bring to a simmer, scraping up any browned bits from the bottom of the pan. Let it cook for 1-2 minutes to reduce slightly.
Step 6: Add the lemon juice and lemon zest to the skillet. Stir well.
Step 7: Add the drained pasta to the skillet with the sauce. Toss to combine. If the sauce seems too thick, add a splash or two of the reserved pasta water until it reaches your desired consistency.
Step 8: Return the cooked shrimp to the pan. Add the fresh parsley. Toss gently to combine and heat through for about 1 minute.
Step 9: Taste and adjust seasoning with salt and pepper as needed. Serve immediately, topped with grated Parmesan cheese if desired.