Preheat the oven to 375 degrees F (190 degrees C). Coat a large baking dish with oil or cooking spray.
Cut pumpkin in half, and remove seeds; cut into 1/4 inch thick slices. Peel slices, and place pumpkin slices into a large bowl. Toss with onion and melted butter, and season with salt and white pepper. Arrange in prepared baking dish.
Bake pumpkin in preheated oven for 30 minutes. In a mixing bowl, beat eggs with milk and cheese; pour mixture over pumpkin in baking dish. Continue baking for 20 minutes, or until golden brown.