Spray a piece of foil with cooking spray, press it gently over the frozen pie crust, and place it in the oven to bake for 10 minutes.
Remove the foil and continue to bake for 3-5 minutes.
Remove from the oven. Place the foil on the bottom of a baking sheet. Place the pie crust on top.
Cook the sausage links in a large skillet over medium heat until just cooked and browned on the outside—they will finish cooking in the oven. Place on a paper towel to drain grease, then cut into bites.
Remove the sausage grease from the pan and add olive oil. Once the pan is hot, add the mushrooms and cook without stirring for 2 minutes, then stir and continue cooking for a minute or two. Remove from the heat. Season with sea salt and freshly cracked pepper to taste.
Combine the eggs, milk, sea salt, and freshly cracked pepper to taste in a bowl and whisk until very well combined.
Sprinkle most of the sausage into the bottom of the pie crust, followed by most of the mushrooms and cheese.
Add the well-whisked egg mixture.
Sprinkle the remaining sausage, mushrooms, and cheese on top.
Carefully place in the oven and bake for 30 to 35 minutes, or until the top is set and not wobbly and the eggs are cooked through. Don’t overcook!