Bring a large pot of water to boil, add 1 tablespoon of salt and the pasta to the pot, 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 black pepper and salt to taste, no more than about 1 teaspoon each, 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. Taste sauce for seasoning, then toss the drained pasta with shrimp and sauce, then serve immediately.