Preheat the oven to 450 degrees F (230 degrees C).
Place 10 slices bacon in a large skillet and cook over medium-high heat, turning occasionally, until crispy and evenly browned, 7 to 10 minutes. Drain bacon slices on paper towels and crumble.
Heat butter and olive oil in a same skillet over medium heat. Stir in mushrooms and onion. Add 1/4 teaspoon salt and pepper. Cook, stirring occasionally, until mushrooms and onions are slightly brown and tender, about 8 minutes.
Sprinkle mushroom-onion mixture, crumbled bacon, Swiss cheese, Gruyere cheese, and green onions into the pie crust.
Whisk eggs slightly in a bowl; beat in cream, 3/4 teaspoon salt, garlic powder, sugar, nutmeg, and cayenne pepper. Pour egg mixture carefully into the pie crust.
Thread a toothpick through 1 end of 1 of the remaining bacon slices; roll the bacon around the toothpick to form a rose shape. Repeat with the remaining bacon slices. Arrange bacon roses on top of the quiche.
Bake in the preheated oven for 15 minutes.
Reduce oven temperature to 300 degrees F (150 degrees C). Continue baking until a knife inserted in the middle comes out clean, about 30 minutes more. Cover with aluminum foil if top is getting too brown. Let quiche rest for 10 minutes before cutting.
