Banana-Pineapple Sorbet in a Coconut Shell

In a saucepan, bring the sugar and water to a boil and cook, stirring until the sugar has completely dissolved, about 2 minutes. Remove from heat and let cool. Meanwhile, pare the pineapple, quarter lengthwise and remove the core. Cut into cubes. Peel and slice the banana and place in a bowl with lemon juice. Add the pineapple chunks, transfer to a blender and puree until smooth. Slowly add the sugar syrup and the coconut milk. Beat the egg whites until stiff and fold into the liquid. Pour the mixture into a bowl and freeze 5 hours, stirring every 20-30 minutes with a whisk or a hand blender during the first 3 hours every 20-30 minutes