Preheat the oven to 350°F/180°C. Generously grease a 9x13 inch baking dish with butter or non-stick baking spray and set aside.
Add the peaches, sugar, lemon juice, and all purpose flour to a large bowl. Stir until the peaches are coated.
2 pounds sliced peaches, ⅓ cup granulated sugar, 1 tablespoon lemon juice, ¼ cup all purpose flour
Pour the fruit into the baking dish, spreading into an even layer.
In a separate mixing bowl, whisk the melted butter, sugar, brown sugar, flour, oats, cinnamon, nutmeg, and salt together until crumbly.
½ cup unsalted butter, ¼ cup granulated sugar, ¾ cup brown sugar, ⅔ cup all purpose flour, ⅔ cup whole rolled oats, ½ teaspoon cinnamon, ¼ teaspoon nutmeg, ¼ teaspoon salt
Sprinkle the topping generously and evenly over the peaches.
Bake for 50-60 minutes until the peaches are bubbly and the topping is crisp and golden brown.
Remove from the oven and let cool for 10-20 minutes. Serve with vanilla ice cream and enjoy!