In a large pot of boiling salted water, cook the fettuccine according to package instructions until al dente. Drain and set aside, reserving 1/2 cup of pasta water.
In a large skillet, melt the butter over medium heat. Add the minced garlic and sauté for about 30 seconds until fragrant.
Add the shrimp to the skillet, season with salt, pepper, and red pepper flakes if using. Cook for 2-3 minutes until shrimp are pink and opaque, then remove from the skillet and set aside.
In the same skillet, add heavy cream, lemon zest, and lemon juice. Allow to simmer for 2-3 minutes, stirring frequently.
Gradually stir in the grated Parmesan cheese until melted and combined. If the sauce is too thick, add reserved pasta water a little at a time until desired consistency is reached.
Return the cooked shrimp to the skillet and toss to coat in the creamy sauce. Add the cooked pasta and mix until well combined, heating through for another 1-2 minutes.
Remove from heat, taste, and adjust seasonings as needed. Garnish with fresh chopped parsley before serving.
Notes
Adjust the amount of red pepper flakes to your spice preference.