Preheat oven to 400 degrees F.
Lightly grease a 12-cup standard muffin tin or line with paper liners, also sprayed with non-stick cooking spray. (I usually make 18 muffins with this recipe.)
Place all ingredients (besides mix-ins) in a blender or food processor: oats, bananas, eggs, Greek yogurt, honey, chia seeds, collagen peptides, cinnamon, baking powder, baking soda, vanilla, and salt.
Blend on high for 2-3 minutes, and stop to scrape down the batter from the sides as needed, until batter is smooth and the oats are almost completely broken down.
Add mix-ins by hand after blending is complete, or sprinkle on top once the batter is in muffin cups.
Divide the batter between the prepared muffin cups, filling them about 3/4 full.
Bake for about 15 minutes, or until tops of the muffins set and are golden brown, and a toothpick inserted in the center comes out clean.
Let the muffins cool for about 10 minutes before removing from pan, then dig in!