Start by thawing your frozen shrimp under cool running water for about 3 minutes. Pat them dry with a paper towel. Mince the garlic cloves finely and zest the lemon before cutting it in half for juicing. Set these aside so they are ready to go as soon as the pasta is cooked.

In a large pot or deep skillet, combine the dry pasta, water (or broth), olive oil, minced garlic, salt, and red pepper flakes. Bring the mixture to a boil over high heat. Once boiling, stir frequently to prevent the noodles from sticking. Cook for about 7-8 minutes. When the liquid has mostly reduced into a thick sauce and the pasta is nearly al dente, toss in the shrimp. Cook for another 2-3 minutes until the shrimp turn pink and opaque.

Turn off the heat and immediately stir in the fresh spinach, lemon juice, and lemon zest. The residual heat will wilt the spinach in seconds. Toss everything together so the sauce coats the noodles evenly. Taste and add extra salt or pepper if needed. Divide the pasta into four bowls and top with a sprinkle of parmesan cheese or extra lemon zest for a bright finish.