Preheat oven to 375°F (190°C) and line a 12-cup muffin tin with paper liners or generously grease with cooking spray. Position oven rack in center for even heat distribution.

Pulse ¾ cup of the rolled oats in a food processor until they resemble coarse flour, leaving some texture. The remaining ¾ cup of whole oats will provide texture contrast.

In a large mixing bowl, whisk together the processed oats, remaining whole oats, flour, brown sugar, baking powder, cinnamon, and salt until evenly distributed.

In a separate medium bowl, mash bananas until mostly smooth with a few small chunks remaining. Whisk in the melted coconut oil, eggs, milk, and vanilla extract until cohesive and slightly foamy.

Create a well in center of dry ingredients and pour in banana mixture. Using a rubber spatula, gently fold ingredients together with 8-10 broad strokes until just combined. Divide batter evenly among muffin cups, filling each about ¾ full.

Bake for 18-22 minutes until tops spring back lightly when touched and a toothpick inserted into center emerges with just a few moist crumbs. Tops should be golden brown with slightly darker edges.