Preheat your oven to 350°F (175°C). Grease a 9×13 inch baking dish, or line it with parchment paper.
In a large mixing bowl, combine the flour, rolled oats, sugar, and salt. Cut in the cold butter using a pastry blender or your fingers until the mixture resembles coarse crumbs.
Press about two-thirds of the mixture firmly into the bottom of the prepared dish to form the crust.
Bake the crust in the preheated oven for 15 minutes or until it just begins to turn golden.
Remove the crust from the oven and spread the cherry pie filling evenly over the hot crust.
Crumble the remaining oat mixture over the cherry filling.
Return to the oven and bake for an additional 30 minutes, or until the top is lightly browned and the filling is bubbly.
While the bars cool, whisk together the powdered sugar, milk, and vanilla extract in a small bowl until smooth.
Allow the bars to cool completely in the pan on a wire rack. Once cooled, use the edges of the parchment paper to lift the bars out of the pan, then cut into squares.
