Preheat oven to 400°F. Line 12 muffin cups with paper liners.
Measure oats into a blender. Blend until the oats are ground into a fine powder, like flour. Shake the ground oats to one side of the pitcher and add the baking powder, baking soda, salt, bananas, honey, Greek yogurt, eggs, and vanilla to the blender. Turn on the blender to low speed and then immediately increase to high speed. Blend until the ingredients are just combined, stopping and scraping down the sides of the blender as necessary. If using chocolate chips, add half of them at the very end; sprinkle them on top of the finished batter in the blender and quickly pulse one time to incorporate the chocolate chips without chopping them further.
Evenly divide the batter between the prepared muffin cups, pouring it directly from the blender pitcher. If using, sprinkle the top of each muffin with the remaining chocolate chips. Bake for 14 to 17 minutes or until the muffins test done with a toothpick. Allow the muffins to cool in the pan for 5 minutes, and then transfer them to a wire rack to finish cooling.
To help get the batter going, I grind up the oats and then pick up the blender pitcher and tilt it so that the ground oats are along one side. This way when I add the wet ingredients, some of them make it all the way to the bottom of the pitcher (see the photo at the very top of this post, right below the title). This helps the batter to incorporate more quickly. That being said, if ingredients seem "stuck," you may need to use a spatula to give things a scrape and a stir at the beginning and then proceed with your blending.
I typically use a cookie scoop to fill my muffin cups. However, for blender muffins, I simply poured the batter straight from the pitcher into the paper liners. I did figure out that holding a spoon near the spout of the pitcher (while pouring) helped me to catch the batter and prevent dripping when moving from muffin cup to muffin cup.
You may substitute maple syrup for the honey.
You may use regular yogurt (or even sour cream) instead of Greek yogurt.