Stir together chia seeds and water and let stand for 15 minutes to gel.
Grease muffin tin.
Preheat oven to 350°F.
Grate zucchini with fine grater.
Mash banana until smooth.
In a large mixing bowl, whisk together flours, starch, cocoa powder, baking soda, and salt.
In a small mixing bowl, whisk together zucchini, banana, oil, maple syrup and vanilla. Once chia has gelled, whisk into wet ingredients to combine.
Add wet to dry ingredients and stir to combine.
Add batter to muffin cups 3/4 full and sprinkle with sugar. Bake for 15-20 minutes or until muffins spring back when touched.
Remove from oven and let stand for 2 minutes. Remove muffins from tin and let cool on wire rack.