Preheat the oven to 400 degrees Fahrenheit. Grease a muffin tin with a generous amount of non-stick cooking spray. While the oven is pre-heating, cook the bacon in a large pan over medium heat about 4 minutes per side or until it reaches your desired crispness. Drain any excess grease.
Let the refrigerated pie crust sit at room temperature for about 15 minutes. Lightly dust some flour on a large piece of parchment paper. Lay the pie crust flat and using a cookie cutter or a pint glass, cut circles approximately 2 1/2 to 3 inches in diameter out of the crust. (The measurement does not need to be exact, so long as the piece of crust covers the bottom of the muffin tin and comes up the edges enough to hold the quiche ingredients.) Place each circle of dough in a muffin tin.
Chop the asparagus into one inch pieces. Core, seed, and dice the bell pepper. Roughly chop the mushrooms. Chop the bacon into one inch pieces. Add a couple pieces of each vegetable and bacon, in any combination you like, to each muffin tin. Top each with about 1 teaspoon of the shredded cheese.
In a large bowl, beat eggs and milk until combined. Season generously with salt and pepper. Using a measuring cup (1/3 or 1/4 cup will work best), spoon the egg mixture over each muffin cup until it reaches the top of the crust.
Bake at 400 degrees Fahrenheit for 10 minutes. After 10 minutes, rotate the pan then bake for 5-10 more minutes or until edges of the crust are golden brown, inside of the quiche is firmly set, and a toothpick or fork inserted in the center comes out clean.
Allow to cool then remove from muffin tin. The mini quiches can be served warm, or refrigerated for up to 3 days and reheated for breakfast.