In a bowl, mix berries with granulated sugar, rosewater, and cornstarch, then transfer to a cast iron skillet.
Combine oatmeal, flour, walnuts, butter, brown sugar, and cinnamon; sprinkle over the berries.
Cover loosely with foil and grill for 20-30 minutes until berries bubble and the top is cooked. Cool for 5 minutes, then serve with toppings like ground pistachios and strawberries.
1. Preheat the oven to 375 degrees F. 2. Mix the berries with rosewater, sugar and cornstarch and transfer to an oven-safe baking dish. 3. Make the topping and sprinkle it on the berries. 4. Bake in the oven for 30 to 40 minutes until the topping is fully cooked and golden.