Add the cherries, sugar, and corn starch to a cast iron skillet.
Heat over medium high heat for approximately 15 minutes, stirring consistently.
Allow the cherries to break down and the sauce to thicken. You'll want to use less sugar if your cherries are very sweet, but use the full ½ cup if your cherries are tart.
Once the cherry mixture is complete, remove it from the heat and set it aside.
In a separate mixing bowl, mix together the oats, flour, cinnamon, brown sugar, butter, and vanilla extract. It usually works best to mix together with your fingers. Make sure it is completely combined.
Sprinkle the topping mix over the cherry mixture.
Bake for 25-30 minutes, just until the topping is golden brown.