In a large pot of salted boiling water, cook the spaghetti or linguine according to package instructions until al dente. Reserve 1/2 cup of the pasta cooking water and then drain the pasta and set aside.
In a large skillet, heat the olive oil and butter over medium heat. Add the minced garlic and red pepper flakes (if using) and sauté for about 1 minute or until fragrant, being careful not to let it burn.
Add the shrimp to the skillet. Season with salt and pepper and cook for 2-3 minutes on each side, or until the shrimp turn pink and opaque.
Add the cooked pasta to the skillet with the shrimp. Pour in the lemon juice and zest, along with the reserved pasta cooking water, and toss everything together to coat the pasta evenly.
Stir in the chopped parsley, adjust seasoning with salt and pepper if needed, and toss again. Serve immediately with grated Parmesan cheese on top.
Notes
Adjust the red pepper flakes to your spice preference.