Spray one of the foil pie pans with the nonstick spray.
Place the peaches and berries in a large bowl. Sprinkle with the sugar, cornstarch, lemon juice, and zest. Toss to combine.
Unroll the pie crust and place it in the foil pan. Fill the center of the crust with the fruit mixture and fold the edges up to form a rustic crust. Brush the edges of the crust with the beaten egg and sprinkle with sugar. This will help to promote the browning of the crust.
Place a second foil pie plate or square baking pan upside down on the grill. Place the pie (in its pan) on top of the inverted pan and close the lid to the grill.
Cook until the crust is cooked through, 20 to 30 minutes depending on the temperature of your grill. Check it at 20 minutes and then every five minutes until done.
Serve warm with a scoop of your favorite ice cream.