HEAT OVEN TO 350F/176.7C: Crumple a parchment paper into a ball. Smooth it out and line a 9 x 5 inch loaf pan (23x13 cm) or 4 x 8 inch loaf pan (20x10 cm). Alternatively, spray a loaf pan with oil or line with aluminum foil.
BOWL #1 (small bowl): Mix together mashed bananas, yogurt and baking soda with a fork or spoon.
BOWL #2 (medium bowl or 2 cup measuring cup): Stir together flour, baking powder and salt (if using).
BOWL #3 (large bowl): Use a spoon or whisk to mix butter and brown sugar together until well combined. Add egg and vanilla and whisk until smooth and creamy. Add the banana-yogurt mixture and mix well. Add flour mixture in 3 parts, mixing lightly between each addition. DO NOT over mix. Just mix until flour is incorporated. Batter will be thick. Stir in optional add-in if using.
BAKE: Spoon batter into parchment-lined loaf pan. Bake for 50-60 minutes or until cake tester or toothpick comes out clean. Using the smaller loaf pan size may take a bit longer. Note that most ovens are not very accurate - so start checking after 50-55 minutes. The middle may still be wet. Bake another 3-5 minutes and check again. When done, remove pan from oven and let cool for 10 minutes. Lift banana bread out by holding onto sides of parchment, then cool further. Eat it while still a bit warm!