Preheat the oven to 350°F (175°C). Grease a cake pan with coconut oil.

In a mixing bowl, mash the bananas with a fork. Add the chopped walnuts, flour, baking powder, baking soda, salt, and cinnamon. Mix well.

In a separate bowl, whisk together the eggs, honey, vanilla extract, Greek yogurt, and melted coconut oil. Pour the wet ingredients into the banana mixture and stir until well combined.

Pour the batter into the greased cake pan. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Remove from the oven and let cool before serving.