Preheat the oven to 350ºF.
Make the filling: In a large bowl, combine the berries, maple syrup (or honey), arrowroot, lemon juice, and vanilla. Stir gently until evenly coated.
4 cups fresh strawberries, 4 tablespoons maple syrup or honey, 2 tablespoons arrowroot flour, 1 teaspoon lemon juice, 1 teaspoon vanilla extract
Assemble: Pour the fruit mixture (and any juices) into a 9x9-inch or similarly sized baking dish.
Make the topping: In a separate bowl, mix together the oat flour, rolled oats, coconut sugar, cinnamon, and sea salt. Add the melted butter, maple syrup, vanilla, and lemon zest. Stir until the mixture forms a crumbly topping.
2 cups oat flour, 1 cup rolled oats, ⅔ cup coconut sugar or maple sugar, 1 teaspoon ground cinnamon, ½ cup unsalted butter, 4 tablespoons maple syrup or honey, 1 teaspoon vanilla extract, Pinch of sea salt, Zest of 1 lemon
Bake: Sprinkle the topping evenly over the fruit. Bake for about 55 minutes, until the fruit is bubbling and the topping is golden brown. If the topping browns too quickly, tent the dish with foil for the last 10–15 minutes.
Cool slightly before serving. Enjoy as is, or top with coconut whipped cream or ice cream, if desired.