Preheat your oven to 425 degrees F and line a sheet pan with parchment paper.

In a large skillet, heat 3 tablespoons of olive oil over medium heat. Add the leeks, salt, pepper, and red pepper flakes. Cook for about 4 minutes, stirring occasionally, until the leeks become soft and fragrant.

Push the leeks to the edges of the skillet and add the remaining 1 tablespoon of olive oil and the mushrooms to the center. Cook for about 10 minutes, stirring occasionally, until the mushrooms release their moisture and become deeply browned. Keep the leeks on the outer edges during this process.

Stir in the thyme leaves and frozen peas, cooking for 1 additional minute to combine the ingredients together. Set the filling aside and allow it to cool slightly.

Meanwhile, roll out the pie dough and place it on the prepared sheet pan. Sprinkle the nutritional yeast evenly over the dough, pressing lightly to ensure it adheres.

Spoon the mushroom-leek mixture onto the center of the dough, spreading it evenly while leaving a 1-inch border around the edges. Fold the edges over the filling, overlapping sections as you go to create a rustic crust.

Brush the crust with the whisked egg and sprinkle with flaky sea salt for added crunch and flavor.

Bake in the oven for 20-25 minutes, or until the crust is golden brown and the filling is bubbly and aromatic. Serve warm and enjoy!