In a small bowl, stir together all the filling ingredients. Fill a half-pint Mason jar or an eight-ounce ramekin with the mixture, pressing down with clean hands or the back of a spoon to really pack it in and create juice. Set aside.

To make the topping, in another small bowl, mix together the flour, oats, brown sugar and cinnamon. Pour in the melted butter and stir until evenly moistened.

Sprinkle the topping over the peaches, mounding up as high as possible.

Place the jar or ramekin on a small baking sheet to collect juices, and bake in the preheated oven for 20-25 minutes, or until the filling is bubbly and the top is golden brown. Let cool for 10-15 minutes before serving.