Preheat the oven to 425°F (220°C). Lightly dust a working surface with flour. Remove pie crusts from the package and unroll, stacking them on top of each other. Roll out to a 17 by 12-inch rectangle.
Transfer and fit the crust into a 15 by 10 by 1-inch jelly roll pan, pressing gently. Fold crust edges under and decorate as desired. Chill in the refrigerator until ready to fill.
For the topping: In a mixing bowl, combine granulated sugar, brown sugar, oats, flour, and salt. Add the chilled butter and cut it into the mixture with a pastry cutter until crumbly. Refrigerate the topping until needed.
For the filling: In a small bowl, whisk together the granulated sugar, brown sugar, flour, cinnamon, nutmeg, and salt. Toss the sliced apples with lemon juice, then coat them with the sugar mixture.
Assemble the pie: Spread the apple mixture evenly over the prepared crust, pressing gently. Sprinkle the chilled topping evenly over the apples.
Bake in preheated oven for 33-38 minutes, tenting with foil during the last 10 minutes to prevent excessive browning. The pie is done when the apples are tender when pierced with a toothpick. Remove from oven and let cool.
Optional glaze: Whisk powdered sugar with half and half until thick but pourable. Drizzle over the cooled pie before cutting into squares.