Preheat the oven to 375 F.
Grease the muffin tin. To make the mini quiche crust shape, either use a 2.5 inch cookie cutter to cut the crust, then gently press the cut crusts into the muffin tin OR if you don't have that size cookie cutter, lay the pie crust over the muffin tin, press the crust into the tin, and cut around the edges to form a muffin shape.
Cook the bacon in a pan, and remove once cooked. Drain some bacon grease, leaving just enough to thinly coat the pan. Sauté the mushrooms in the same pan with the bacon grease until golden brown. Add spinach the last few minutes until wilted.
Use 1 cup of the gruyere cheese and sprinkle at the bottom of the pie crust.
Whisk together the eggs, milk, pepper, salt, and garlic powder. Then, fold in the bacon, mushrooms, spinach, and green onions.
Pour the egg mixture evenly between each quiche, then sprinkle the remaining cheese on top.
Place the muffin tin in the oven, and bake for 20-25 minutes, until the tops are golden brown.
Let cool for 5 minutes then remove the quiches from the muffin tin. Enjoy!