Start your Grill on 'smoke' with the lid open until a fire is established in the burn pot (3-4 minutes). Preheat to 425F.
Cut the onion in half and place on the grates of the grill. If you're using fresh chicken breasts, barbecue the chicken at the same time as the onions. The chicken is fully cooked when the internal temperature reached 170F. While the onion and chicken are cooking, prepare the pie crust by putting one crust in a pie plate. When the chicken and onions are done, shred chicken and chop onion into small pieces and place in the prepared pie plate along with the mixed vegetables.
Combine cream of chicken soup, mayo, sour cream, and curry powder in a bowl. Pour into the pie crust with the chicken and mix to combine. Wet the sides of the bottom crust with a small amount of water and top with the second pie crust. Push gently along the sides of the crust to seal the two pie crusts together.
Place in the and bake for 40 minutes, or until the crust is golden brown. Serve hot.