Preheat your oven to 350°F (175°C).
Prepare the apples by peeling, coring, and slicing them thinly.
In a large bowl, combine sliced apples, granulated sugar, lemon juice, ground cinnamon, and salt. Toss to coat the apples well.
Transfer the apple mixture to a greased baking dish, spreading it evenly.
In a separate bowl, mix together flour, rolled oats, brown sugar, melted butter, and baking powder until crumbly.
Sprinkle the topping evenly over the apple mixture in the baking dish.
Bake in the preheated oven for 40-45 minutes, or until the top is golden brown and the apples are bubbling.
Let the cobbler cool for at least 15 minutes before serving.