Preheat oven to 350F. Prepare a 9x5 loaf pan with parchment paper.
In a large mixing bowl, mash bananas with a fork. Whisk in eggs, creamy peanut butter, melted coconut oil, maple syrup and vanilla.
Add in oat flour, baking powder, baking soda and sea salt. Mix in chocolate chips and crushed walnuts until just combined.
Transfer half of the batter into another bowl and add 1/4 cup cacao powder, mix well.
Using a large spoon, add batters alternately into loaf pan. When all batter is in pan, use a knife to swirl the tops, about 2-3 times through. Top with extra crushed walnuts and chocolate chips.
Bake for 50-55 minutes or until toothpick inserted in center comes out clean. Leave in loaf pan for 10 minutes before transferring to a cooling rack to cool for 15 minutes before cutting into slices.