Preheat oven to 190°C. Lightly grease an ovenproof dish with a little melted butter.
Combine flour with 1 teaspoon cinnamon powder in a mixing bowl. Rub in the butter until mixture resembles coarse breadcrumbs. Add half of the soft brown sugar and oats to mix into a crumble mixture.
Core the apples and cut into quarters then into wedges.
Arrange the apple wedges in the prepared greased dish. Pour the lemon juice over and toss well to coat. Combine remaining soft brown sugar with the rest of the cinnamon powder; sprinkle mixture over the apples. Toss well to combine. Sprinkle the crumble mixture evenly over the top to completely cover the apples.
Put the dish on a baking tray. Bake in preheated oven for 30-35 minutes or until the crumble topping is golden and the apples are tender when tested with a skewer. Serve this warm with ice-cream if desired.