1. Filling: Heat oil in large skillet on medium-high heat. Add and saute onions for 2 minutes. Add the broccoli, sweet potato, carrot, corn, and peas. Season with salt and pepper. Cook until the vegetables are tender, but not mushy. Set aside.
2. Roux: In a sauce pan on medium-high heat, put oil and margarine. Once the margarine is melted, mix in 1 tablespoon of flour at a time with a whisk. It's done once the it is no longer white and a light brown color. Add veggie stock. Whisk it all together. Let it simmer a bit to thicken. If this doesn't thicken it enough to be a sauce, dissolve cornstarch into cold water and then mix into roux.
3. Add the sauce to vegetable mixture. Stir and taste for seasoning.
4. Pour mixture into pre-baked pie shell. Place the other pie crust on top. Cut slits and in the oven it goes.
5. Bake at 350 degrees F for 14 to 20 minutes, or until the top pie crust has has lightly browned.
Source of recipe: Made this while cooking in the kitchen.