Preheat the oven to 350F. Grease a 9" round baking dish with butter.
Add apples, lemon zest and juice, sugar, cinnamon and nutmeg to a large bowl. Toss until evenly coated and pour into prepared pan.
In a medium bowl, whisk together the flour, sugars, oatmeal, and salt. Using your fingers press the butter into the mixture until big crumbs form. Sprinkle over the apples.
Bake for 45 min-1 hr until brown and bubbly. Remove from the oven, let cool for about 30 minutes. Serve with your favorite ice cream.
