Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente, usually about 8-10 minutes. Stir occasionally to prevent sticking.

Once cooked, reserve 1 cup of pasta water, then drain the spaghetti in a colander and set aside.

In a large skillet, heat the olive oil over medium heat. Add the minced garlic and red pepper flakes, sautéing for about 30 seconds until fragrant. This step infuses the oil with flavor.

Add the shrimp to the skillet in a single layer. Cook for 2-3 minutes on one side until they turn pink, then flip and cook for another 2-3 minutes until fully cooked. Be careful not to overcook them, as they can become rubbery.

Reduce the heat to low and add the lemon zest, lemon juice, and chicken broth to the skillet. Stir well to combine, scraping any browned bits from the bottom of the pan for added flavor.

If using, stir in the heavy cream and let the sauce simmer for 2-3 minutes to thicken slightly.

Add the cooked spaghetti to the skillet, tossing to coat the pasta in the sauce. If the sauce is too thick, add reserved pasta water a little at a time until desired consistency is reached.

Stir in the grated parmesan cheese until melted and creamy. Taste and adjust seasoning with salt and pepper as needed.

Divide the lemon shrimp pasta among plates. Garnish with chopped parsley and additional parmesan cheese if desired. Serve immediately for the best flavor and texture.