Preheat oven to 350℉.
Evenly spread sliced apples in a greased 13x9 baking dish.
In a medium bowl, stir oats, sugar, flour, cinnamon, and salt with a fork until thoroughly mixed.
Pour melted butter over mixture and stir until all butter is absorbed into dry ingredients, and sprinkle evenly over apples in baking dish.
Bake in oven for 35-45 minutes or until apples are tender and topping is crisp and brown.
Let cool for 10-15 minutes and then serve warm. Can be topped with ice cream and caramel topping.