Preheat the oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or grease it lightly.
In a large bowl, combine the rolled oats, whole wheat flour, brewer’s yeast, ground flaxseed, baking powder, baking soda, salt, and ground cinnamon. Stir well to mix all dry ingredients evenly.
In a separate medium bowl, mash the ripe bananas thoroughly with a fork.
Add honey, unsweetened applesauce, plain Greek yogurt, vegetable oil, eggs, vanilla extract, and milk to the mashed bananas. Whisk together until the mixture is smooth and well combined.
Pour the wet ingredients into the bowl with the dry ingredients. Gently fold the mixture together using a spatula or wooden spoon until just combined. Do not overmix; some lumps are okay.
Divide the batter evenly among the 12 muffin cups, filling each about 3/4 full.
Bake in the preheated oven for 18 to 20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and allow them to cool in the tin for 5 minutes.
Transfer the muffins to a wire rack to cool completely before serving.