1. Preheat the grill to 400 degrees.
2. While the grill is preheating, add the butter and onions to a saucepot over high heat and sauté the onions until tender. 
3. Next, add the flour, stirring until combined. Gradually pour in the chicken broth in batches, stirring as needed to prevent clumping.
4. Once the mixture is well combined and has a smooth consistency, mix in the heavy cream.
5. Add in the chicken, vegetables, and poultry seasoning. Once combined, turn off the heat source and set aside.
6. Roll out both pie crusts to fit your skillet. Spray the skillet with cooking spray and add one of the crusts, filling with the chicken pot pie mixture. Lay the second crust over the top, trimming any excess with a knife or scissors as needed. Pinch the edges and cut several slits in the pie crust. 
7. Finally, brush the top of the crust with the egg wash for a golden-brown finish.
8. Once the grill has preheated and the pie is ready, place the skillet on the grill for 45 minutes.
9. Once the crust is golden brown and the pie begins to bubble, the pie is finished! Set the skillet aside and allow it to rest for 15 minutes. Turn off the grill. Serve and enjoy!

Note: If the turkey pot pie is cooked through, but you feel it needs more browning on top, simply broil it for 30 seconds.