01 - Bring a large pot of salted water to a boil. Cook spaghetti until al dente according to package instructions. Reserve 1/2 cup of pasta water, then drain.
02 - Pat the shrimp dry and season with salt and black pepper.
03 - Heat olive oil in a large skillet over medium-high heat. Add shrimp in a single layer and cook 1–2 minutes per side until pink and opaque. Remove shrimp and set aside.
04 - In the same skillet, add minced garlic and red pepper flakes if using. Sauté for 30 seconds until fragrant without browning.
05 - Pour in white wine or chicken broth and scrape up browned bits from the skillet. Simmer for 2–3 minutes to reduce slightly.
06 - Stir in lemon zest, lemon juice, and baby spinach. Toss until spinach wilts, about 1 minute.
07 - Return shrimp to the skillet. Add drained pasta, butter, and Parmesan cheese. Toss thoroughly, adding reserved pasta water as needed to create a smooth sauce.
08 - Remove from heat, stir in chopped parsley, and adjust seasoning with additional lemon juice, salt, or pepper if desired. Serve immediately with extra Parmesan and a drizzle of olive oil.