Grease a 9- by 13-inch baking dish. Preheat oven to 350°F.
In large bowl, mix together fruit, sugar, lemon zest, and juice.
Place fruit mixture in the baking dish.
In a separate bowl, combine all of the streusel ingredients. Use your fingertips to blend mixture together. Sprinkle the mixture over fruit.
Bake for 45 minutes or until topping is golden brown and fruit is bubbling.
Serve with ice cream or whipped cream, as desired.
Technique tip: Reduce the amount of sugar in the filling if your berries are very sweet. Make streusel ahead of time and put in zip-lock bag in freezer. It's OK if the streusel is frozen when placed on berries before baking.