Bring a large pot of water to boil, add 1 tablespoon of salt and the pasta, and cook for 7 to 10 minutes, or according to the directions on the package.
While pasta is cooking, heat olive oil and butter in a large saute pan or skillet over medium heat. Add garlic and cook until fragrant, stirring frequently for about 30 seconds to 1 minute.
Add the shrimp, season them with about 1 teaspoon black pepper and salt to taste, and let sear for 2 minutes on one side, until it's just turning pink, then flip onto their other sides.
Pour in wine or broth, add red pepper flakes, and bring to a simmer for 2-3 minutes, stirring often; the wine will be reduced and the shrimp cooked through by 3 minutes, don't overcook the shrimp.
Take off heat and stir in the lemon slices, lemon zest, lemon juice and parsley. Toss the drained pasta with shrimp and sauce, then serve immediately.