Heat the oven to 375° F.
In a small, microwave-safe bowl, melt the coconut oil in the microwave (30-60seconds) and set aside to cool.
Add the blueberries either to a large bowl or your baking dish. Add the arrowroot, honey, lemon juice, lemon zest and salt. Toss with your hands or a spatula until all the berries are evenly coated. If tossing in a bowl, spoon into a 8x8" square baking dish (or any 2-quart baking dish). Spread the berries out in an even layer.
In a large bowl, whisk the almond flour, arrowroot, salt and baking soda until combined.
In a medium bowl, whisk the melted and cooled coconut oil, egg, egg white, honey and lemon juice until combined.
Add the wet ingredients to the dry ingredients and stir with a spatula until completely blended. The batter will be a bit wet and sticky.
Scoop the batter onto the berries in the baking dish and spread into an even layer. If the topping is too sticky, get your hands or spatula slightly damp with water and then spread it out.
Bake for 30-35 minutes, until the top is golden brown and the edges are bubbling. Let cool for at least 20 minutes (the filling will thicken more the longer it cools), then serve with vanilla ice cream or yogurt.