Preheat oven to 375°F (190°C).
Combine sliced apples with sugars, flour, spices, lemon juice, and melted butter. Toss well and let sit for 10-15 minutes.
Prepare crumb topping by combining flour, oats, brown sugar, salt, and cinnamon. Cut in cold butter until crumbly.
Transfer apple mixture into a buttered baking dish and spread evenly.
Top evenly with crumb mixture. Bake for 35-45 minutes, until topping is golden brown and apples are bubbling.
Cool for 15-20 minutes before serving. Serve warm with vanilla ice cream or whipped cream.