Preheat your oven to 375 degrees F. Grease a 9x9 inch baking dish with butter or non-stick spray.
In a large bowl, toss the sliced peaches and chopped strawberries with granulated sugar, lemon juice, and cornstarch until well coated.
Pour the fruit mixture into your prepared baking dish and spread evenly.
In a medium bowl, combine flour, brown sugar, oats, cinnamon, and salt.
Add the cold cubed butter and work it in using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
Sprinkle the crumb topping evenly over the fruit mixture, making sure to cover all the fruit.
Bake for 35 to 40 minutes until the fruit filling is bubbling around the edges and the topping is golden brown.
Let it cool for about 10 minutes before serving. Serve warm with vanilla ice cream if desired.
