Preheat oven to 425 degrees F (220 degrees C).

Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain bacon slices on paper towels; crumble. Reserve about 2 tablespoons bacon drippings in the skillet.

Cook and stir onion and garlic in reserved bacon drippings over medium heat until onion is softened, 5 to 10 minutes.

Place thawed pie crust in a pie dish; prick holes in the bottom and sides of crust using a fork.

Bake crust in the preheated oven until lightly browned, about 8 minutes. Remove crust from oven and reduce oven temperature to 325 degrees F (165 degrees C).

Whisk half-and-half and sour cream together in a bowl; beat eggs into half-and-half mixture. Mix Swiss cheese, salt, black pepper, and cayenne pepper into half-and-half mixture; add bacon, onion mixture, and parsley. Pour mixture into the crust.

Bake in the preheated oven until a knife inserted into the center of the quiche comes out clean, about 45 to 50 minutes. Cool for 10 minutes before slicing into wedges.