Preheat oven to 350°F (177°C). Lightly grease a 9×13-inch baking pan. Any 3.5-4-quart baking dish works.

Mix all of the filling ingredients together in a large bowl, then spread into the baking pan.

Whisk the flour, brown sugar, and cinnamon together in a medium bowl. Cut in the butter using a pastry cutter or fork until the mixture becomes super crumbly. Stir in the oats. Sprinkle over filling.

Bake for 45 minutes or until the topping is golden brown and the fruit juices are bubbling around the edges. Remove from the oven, place on a wire rack, and allow to cool for at least 5 minutes before serving. Serve warm, room temperature, or cold; plain or with salted caramel and/or vanilla ice cream.

Cover leftovers and store in the refrigerator for up to 5 days.