Preheat oven to 350 and line a 9x5 loaf pan with parchment paper.
Combine bananas, yogurt, peanut butter, butter and eggs in a large bowl (or in the bowl of stand mixer) and beat at medium speed until well blended. Add sugars and beat until light and creamy.
In a small bowl combine flour, flaxseed, baking soda, salt and spices. Whisk briefly to combine.
Add flour mixture to banana mixture and stir until just blended. Add two tablespoons of the peanuts to the batter and gently stir.
Pour batter into prepared baking pan. Sprinkle remaining chopped peanuts on top of loaf and bake at 350 for 1 hour and 5 minutes, or until a toothpick comes out of the centre clean.
Remove from the oven and allow to cool for 10 minutes in the pan before removing to continue cooling on a wire rack.