Stir together the chia seeds, coconut milk, maple syrup, vanilla, and coconut oil in a small bowl. Let set while you preheat the oven to 400°F and grease a 24-cup mini muffin tin with nonstick spray.
Smash bananas with a fork and set aside. In a medium bowl, stir together the flour, cocoa powder, baking powder, and salt.
Add the chia mixture and the bananas to the dry ingredients and mix thoroughly. Spoon into the prepared muffin tin, filling right about to the edge.
Bake for 14-16 minutes until a toothpick inserted into the center of a muffin comes out clean. Remove from tin, using a paring knife around the edges as needed, and let cool on a wire rack.
Serve warm, at room temperature, or chilled.