01 - Boil linguine or spaghetti in a large pot of salted water until al dente. Reserve 1/2 cup pasta water before draining.
02 - Sprinkle shrimp with kosher salt and freshly ground black pepper evenly.
03 - Heat olive oil in a large skillet over medium-high heat. Cook shrimp in a single layer for 1 to 2 minutes on each side until opaque. Transfer to a plate.
04 - In the same skillet, add minced garlic and optional red pepper flakes. Cook for 30 seconds until fragrant.
05 - Pour in white wine or chicken broth, scraping browned bits from the skillet. Simmer for 2 minutes to reduce slightly.
06 - Stir in lemon zest and juice, then add fresh spinach. Cook until spinach wilts, approximately 1 minute.
07 - Return shrimp to skillet, add drained pasta and unsalted butter. Toss well, adding reserved pasta water gradually to form a smooth sauce.
08 - Remove from heat, sprinkle with chopped parsley. Serve immediately, optionally topped with grated Parmesan cheese.