Preheat the oven to 180C/350F/Gas 4. Grease and line a 9x5-inch loaf pan with parchment paper. Set aside.
In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
In a separate large bowl, whisk together the eggs and sugar until thick and lighter in colour.
Add the yogurt, oil, vanilla, bananas, and peanut butter, and whisk until combined.
Add the dry ingredients in thirds and fold in until just combined - do not overmix. The mixture will be thick and somewhat lumpy.
Pour the batter into the prepared pan and spread out evenly.
Optional: Drizzle 2 tablespoons of peanut butter over the top of the batter. (If your peanut butter is too thick to drizzle, microwave it for a few seconds until runny.) Use a knife or toothpick/cake tester to swirl the peanut butter into the top of the batter.
Bake for about 60 - 70 minutes, or until a toothpick/cake tester inserted into the centre comes out clean with a few moist crumbs.
Allow to cool completely in the pan on a wire rack before slicing and serving.
Notes
Bread stays fresh in an airtight container at room temperature or in the fridge for up to 5 days. It also freezes well for up to 3 months. Thaw overnight in the fridge.