Preheat oven to 350ยบ F. In a large bowl, gently combine the blueberries, strawberries, lemon juice, maple syrup, vanilla, and arrowroot flour. Stir gently but thoroughly so that everything is well-coated. Pour into a 9-inch pie dish or baking dish.
In another large bowl, combine the oats, flour, salt, cinnamon, and nutmeg. Pour the melted butter over the top followed by 1/3 cup maple syrup. Mix together thoroughly. Add the coconut sugar and pecans, and work it into the topping until it feels crumbly.
Scoop the crumb topping on top of the berries in large mounds, and spread the mixture across the top evenly.
Bake for 45 minutes, or until golden brown. Serve warm with vanilla ice cream, or let cool completely and store in the fridge for up to seven days. Enjoy!