Place the apple chunks in a large bowl, along with the berries (if using) and lemon zest.
Toss with the lemon juice and sugar.
Transfer to the prepared baking dish.
Spread the topping evenly over the apples.
Bake for approximately 30-40 minutes, or until bubbly and the topping is golden brown.
Remove from oven and place on a wire rack to cool for about 30 minutes before serving.
Serve with softly whipped cream or vanilla ice cream.