Stir together all ingredients for the walnut topping in a small bowl and set aside until ready to use.
Preheat the oven to 350 degrees F and line a 9" x 5" loaf pan with parchment paper.
Mash the bananas in a mixing bowl. Whisk in the eggs, pure maple syrup, and vanilla extract. Stir until well-combined.
In a separate bowl, stir together the remaining (dry) ingredients. Transfer the dry ingredients to the mixing bowl with the wet and stir until well combined.
Pour half of the banana bread batter into the prepared loaf pan. Sprinkle with half of the walnut topping, creating an even layer. Repeat for remaining banana bread batter and walnut topping.
Bake on the center rack of the preheated oven for 50 to 55 minutes, until golden-brown around the edges and firm in the center. Turn off the oven and leave bread in the warm oven another 10 minutes.
Remove coffee cake banana bread from the oven and allow it to cool at least 30 minutes before slicing and serving.
*To make recipe vegan, replace the eggs with flax "eggs." Stir together 2 Tbsp ground flax seed and 6 Tbsp water in a small bowl. Allow this mixture to sit, stirring occasionally, for 15 minutes, or until it reaches the consistency of beaten eggs. Proceed with the recipe as normal using the thickened flax "egg" mixture in place of regular eggs.