Preheat your oven to 375°F (190°C). Roll out the pie crust and fit it into a deep pie dish, ensuring it covers the edges. Brush the crust with olive oil and pre-bake for about 8 minutes until slightly golden. Set aside to cool.

In a large skillet, heat 1 tablespoon olive oil over medium heat. Add chopped onion and minced garlic, sautéing until translucent. Add the ground sausage, breaking it up with a spoon, and cook until browned. Drain excess fat. Stir in pizza sauce, shredded mozzarella cheese, pepperoni slices, diced bell peppers, and sliced mushrooms. Season with Italian seasoning, salt, and pepper to taste. Cook until the cheese begins to melt.

Spoon the filling into the pre-baked crust, spreading it evenly. Top with extra mozzarella cheese and pepperoni slices. Optionally, add a top crust, sealing the edges and cutting slits for steam release.

Place the assembled pie in the preheated oven and bake for 25-30 minutes, or until the crust is golden and the filling is bubbly.

Allow the pie to cool slightly to let the filling set. Slice and serve warm, enjoying the rich, cheesy, and savory flavors.