Preheat oven to 375°F.
Peel and chop carrots and butternut squash if applicable (A 1.5 pound squash should suffice if buying whole); dice the onion. Place veggies on a roasting pan. Drizzle with olive oil and sprinkle with salt and pepper. Roast 30 minutes or until tender when poked with a fork but still firm in the middle.
Add green beans to the pan and toss to coat with the oil. Return to the oven and roast until beans are tender crisp, about 5 minutes longer.
Stir in the peas and set aside.
Heat butter in a large pot over medium-low heat. Add the flour and cook for 1 minute, whisking constantly. Whisk in the milk until smooth. Whisk in the vegetable broth, parsley, and thyme. Simmer until thickened, about 3 minutes.
Stir the vegetables into the sauce. Season to taste with remaining salt and pepper.
Spray pie plate with cooking spray and line with pie crust. Fill with the vegetable mixture and cover with second pie crust.
Bake uncovered until dough is golden brown, about 45 minutes. Allow to cool for 5-10 minutes before serving.