Preheat the oven to 350 and line a baking sheet with parchment
Core the apples with an apple corer, spoon, or melon scoop
Place the flour, sugar, oats, cinnamon, and salt into a mixing bowl. Drizzle in the melted butter. Use your hands to incorporate everything until you have a crumbly, streusel-style mixture
Spoon the filling into the cored apples. Try to pack them a little, but don’t press or fill them with too much force. Spoon any leftover streusel onto the baking sheet to bake with the apples (sort of like granola!)
Bake the apples for 30-40 minutes (this will depend on the size of the apples), or until the top of the filling is browning and the apples are easily pierced with a paring knife.
Bonus: If you’d like to make this recipe gluten-free, you can use a GLUTEN FREE, UNBLEACHED FLOUR in place of all-purpose flour.