Add shrimp to the skillet and season with salt, pepper, and optionally, red pepper flakes. Cook until shrimp are pink and cooked through, about 3-5 minutes.
Stir in lemon juice and zest, mixing well to infuse the shrimp with a bright, citrusy flavor.
Add the cooked spaghetti to the skillet, tossing to combine with the shrimp and sauce, ensuring every strand is coated.
Remove from heat, stir in fresh parsley, and serve immediately for the best flavor and texture.
Notes
For a lighter version, substitute butter with olive oil. This dish complements well with a green salad and a chilled glass of white wine.