Preheat the oven to 350° and grease a 9x5x3-inch loaf pan with non-stick spray or butter.
Add softened butter and sugar to a mixing bowl and beat with an electric mixer at medium speed until light and fluffy. (About 5 minutes.)
Add the eggs, one by one, beating until well-combined.
Sift in the flour, baking soda, protein powder, baking powder, brown sugar, and salt and beat until just combined, about 1-2 minutes.
Add the mashed bananas, Greek yogurt, and vanilla. Mix with a rubber spatula, then stir in the nuts.
Pour the batter into the greased pan and bake for 1 hour or until a toothpick inserted into the center comes out clean. Let the bread cool in the pan for 10 minutes. Then transfer it onto a wire rack to finish cooling. Slice, serve, and enjoy!
