Wisk almond milk and ½ cup of almond milk in a small bowl thoroughly. Let sit in fridge for 10minutes.
Add bananas and the remaining 1 cup of almond milk to a blender. Blend until smooth, scraping down the sides of the blender as need.
Add mangoes, blending until smooth.
Take the chia seed mixture out of the fridge—it should have thickened to a gel-like consistency. Give it another good whisk. Using a rubber spatula or spoon, scrape the chia seed mixture out of the cup and into the blender. Blend until smooth.