Preheat oven to 425 degrees F. Prepare a 9 x 9 inch round pie pan with unbaked pie crust. I like to crinkle the crust with my fingers at the top for decoration (this is optional). You can also crimp the edges of the crust with a fork. Place in the refrigerator until ready to use.
In a large mixing bowl, combine peaches, sugars, flour, cinnamon, nutmeg and lemon juice. Mix to combine.
In a medium bowl add butter cubes, oats, flour, cinnamon and sugars. Mix together with a pastry cutter or fork until crumbly pieces form.
Assemble the pie by spooning the peach mixture into the pie crust, then sprinkle the crumble topping all over the top, spreading to the edges in an even layer.
Bake pie for 15 minutes, then reduce the oven heat to 350 degrees F and bake for an additional 45-50 minutes. Add a pie shield or cover the pie crust with aluminum foil to prevent the crust from burning.
Let the pie cool for at least 3 hours to thicken before serving (optional). Slice and top with vanilla ice cream or whipped cream. Enjoy!