For the fruit filling: In a large bowl, combine the sliced peaches, ⅓ cup of the granulated sugar, ¼ cup of the flour, and the orange juice.
Toss well.
Add the berries and toss lightly.
Pour into a 9 by 12 by 2-inch baking dish.
For the crumble topping: Place the remaining 1 cup of flour, the remaining ⅓ cup of granulated sugar, the brown sugar, and the salt in the bowl of a food processor fitted with a steel blade.
Pulse a few times to combine.
Add the butter and pulse until the butter is the size of peas.
Pour the mixture into a bowl.
Add the oats.
Work it with your hands until it's in large crumbles.
Add ½ cup of chopped walnuts.
Mix well.
Spread the topping evenly over the fruit, making sure the fruit is covered.
Sprinkle with some extra walnuts and sugar.
Bake for 40 minutes, or until the fruit is tender and bubbly and the topping is golden brown.
Serve warm or at room temperature.
Recipe by Kitoula's Greek Food Journal at https://kitoula.com/2013/10/peach-and-berry-crumble-with-walnuts/