Fry the bacon pieces in a large skillet over medium-low heat until crispy. Remove from pan to paper towel to drain. Set aside to cool. Remove grease from pan except for about 2 tablespoons. Fry the onions in the grease until soft, then add mushrooms, and sautee til soft and brown. Remove from pan and set aside to cool. Preheat the oven to 400 degrees. Roll out the pie crust and press it into a large fluted deep tart pan (or a deep dish pie pan). Whip the eggs, cream,chili flakes, salt and pepper in a large bowl. In pie crust, layer mushrooms and onions, bacon, spinach and cheese. Pour the egg mixture into the pie crust over the cheese. Place the pan on a rimmed baking sheet, cover lightly with aluminum foil, and bake it for about 40 to 45 minutes. Remove the foil and continue baking for 10 to 15 minutes, or until the quiche is set and the crust is golden brown. (The quiche will still seem slightly loose, but will continue to set once remove from the oven.) Remove from the oven and allow to sit for 10 to 15 minutes. If using a tart pan, remove the quiche from the pan, cut into slices with a sharp serrated knife, and serve!