Prepare filling: In a large saucepan, simmer apples, cherries, and cider, stirring occasionally, until fruits are softened and plump, about 5 minutes.
Whisk together oats, flour, ¾ cup brown sugar, 1 teaspoon cinnamon, baking soda, and salt, in a large bowl. Cut in butter with a pastry blender or 2 knives until you have pea sized crumbles.