Preheat oven to 375 degrees. In an 8-inch square baking pan, toss apples, lemon juice, and cherries.
Whisk together sugar, a pinch of salt, the cinnamon, and flour. Add half the sugar mixture to apples; stir to combine.
Stir together oats and remaining sugar mixture. Add butter, and stir. Evenly pat oat-butter mixture over apples. Bake until oats are golden, apples are tender, and the juices are bubbling, 40 to 50 minutes.