Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease well.
In a large bowl, whisk together the flour, oats, baking powder, baking soda, cinnamon, nutmeg, and salt.
In a medium bowl, mash the bananas until smooth. Add the honey, eggs, melted coconut oil, Greek yogurt, and vanilla. Whisk until just combined.
Pour the wet ingredients into the dry ingredients. Fold gently with a rubber spatula until no large dry pockets remain — about 20–30 folds. Do NOT overmix. The batter should look thick and slightly rough.
Divide batter evenly among muffin cups, filling each about ¾ full. Top with chopped walnuts, a pinch of rolled oats, and a thin drizzle of honey.
Bake for 20–23 minutes until the tops are deeply golden and a toothpick inserted into the center comes out clean or with a dry crumb.
Cool in the pan for 5 minutes, then transfer to a wire rack.