Pre heat oven to 350F.
In a large bowl combine mango, blueberries, lemon juice, and ginger. Sprinkle in sugar, arrowroot and salt, lightly toss everything together.
Pile fruit mixture into a greased 88 (or 99) baking dish.
In a separate bowl, mix together the oats, walnuts, cinnamon, coconut sugar, salt and cinnamon.
Evenly spread the crisp topping over the mango-blueberry mixture and pop into the oven for 35-40 minutes or until the top is golden brown, the fruit is bubbly and your kitchen smells amazing.
Serve warm, room temperature (or cold!) and top with your favorite ice-cream, whipped cream or yogurt topping. Enjoy!