Prepare the filling: In a bowl, mix blueberries, sugar, cornstarch, and lemon juice until well combined. Let sit for 5 minutes.
Prepare the crust: If using a Dutch oven, line the bottom with the pie crust. For foil packets, cut the crust into 4-6 squares.
Assemble: Pour the blueberry mixture into the crust-lined Dutch oven or onto each foil square. Fold the crust over the filling or top with a second crust piece.
Cook: For a Dutch oven, place in a preheated campfire or camp stove with coals on top and bottom (about 6-8 coals on bottom, 12-14 on top). Cook for 25-30 minutes, rotating occasionally. For foil packets, place on a grate over hot coals and cook for 15-20 minutes, flipping once.
Check for doneness: The filling should be bubbling and the crust golden brown. Let cool for 10 minutes before serving.
Serve: Enjoy warm as is or with a scoop of vanilla ice cream (optional).