Preheat the oven to 350F.
To make the crisp topping, mix together the oats, flours, brown sugar, lemon zest, and salt in a large bowl. Add the butter and working quickly, using your fingertips or a pastry blender or fork, cut the butter into small pieces until a crumbly mixture forms. Refrigerate until ready to use.
Place the sliced stone fruit, berries, cane sugar, and cornstarch in a medium bowl and taste, adding a pinch of salt or more sugar if desired. Toss the fruit gently with your hands to combine the ingredients.
Pour the fruit into a large baking dish or divide between 8 smaller ramekins. Sprinkle the topping over the fruit in an ever layer.
Place the baking dish on a parchment-lined sheet pan and cover with a layer of foil. Bake for 30 minutes, then remove the foil and continue baking until the crisp topping is browned and the fruit is bubbling, about 15-25 minutes longer.
Let cool 20 minutes, then scoop onto plates and serve with creme fraiche.
*To make this recipe gluten-free, opt for gluten free flour and oats; nothing else needs to be modified for the recipe