Preheat oven to 400°F (200°C).

Place pie crust in a 9-inch quiche pan.

Layer mozzarella and cheddar cheese evenly in the pie crust.

Top with pepperoni slices and drained mushrooms.

In a medium bowl, whisk together milk, eggs, Italian seasoning, and minced garlic.

Pour the egg mixture evenly over the mushrooms and pepperoni.

Bake for 40 to 45 minutes, or until a knife inserted near the center comes out clean.

While the quiche is baking, simmer spaghetti sauce over low heat.

Let the quiche cool slightly before slicing.

Cut the quiche into pie slices.

Spoon the warm spaghetti sauce over each slice before serving.