Blend the oats in a high-speed blender until they reach a flour consistency. Add 3 bananas, the eggs, baking powder, cinnamon, salt, and vanilla. Blend until smooth. Pour the batter into a small bowl, stir in the chia seeds, and let sit for about 10 minutes to thicken.
Heat a griddle or skillet covered with nonstick cooking spray over medium-high heat.
Make the pancakes by pouring ¼ cup of batter for each pancake onto the griddle or skillet, leaving about an inch of space between pancakes. While the batter is still runny, add the blueberries to the pancakes. Cook the pancakes until the batter is set, about 2 minutes. Flip and cook on the other side for about 30 seconds.
Repeat step 3 to use all the batter. Slice the remaining banana and top the pancakes with the banana slices. Serve with maple syrup, if desired.