Preheat the oven to 425°F (220°C). Place the bottom crust into a 9-inch pie plate and chill until ready to use.

Heat butter in a large skillet over medium heat. Add onion, celery, tofu, and garlic; cook until onion is tender and translucent, approximately 10–15 minutes. Season with oregano, salt, and black pepper. Stir in flour until the vegetable mixture is coated.

Slowly stir milk into the vegetable mixture and cook until the mixture begins to thicken, about 5 minutes. Add the vegetable broth and cook for another 5 minutes until the mixture thickens. Stir in the frozen vegetables.

Pour the filling into the prepared crust. Top with the remaining pie crust, crimp the edges together to seal, and poke ventilation holes in the top crust.