Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish or equivalent oven-safe casserole dish.

Prepare the cherry filling: In a large bowl, gently combine the pitted cherries, granulated sugar, flour, lemon zest, and lemon juice. Toss until the cherries are evenly coated. Pour the cherry mixture into the prepared baking dish and spread into an even layer.

Prepare the topping: In a separate medium bowl, whisk together the rolled oats, flour, brown sugar, and ground cinnamon until well combined.

Cut in the butter: Add the cold, cubed butter to the dry topping mixture. Using a pastry blender, two knives, or your fingertips, cut the butter into the flour mixture until coarse crumbs form, resembling peas or small pebbles. Do not overmix.

Assemble and bake: Sprinkle the oat topping evenly over the cherry filling layer. Place the dish on a baking sheet (to catch any bubbling overflow) and bake for 40 to 45 minutes, or until the topping is golden brown and the cherry filling is bubbly around the edges.

Let the crisp cool on a wire rack for at least 15-20 minutes before serving. This allows the filling to set slightly. Serve warm, preferably with a scoop of vanilla bean ice cream or fresh whipped cream.