Preheat oven to 180°C. Line a loaf tin with baking paper.
Melt butter. In a bowl, whisk eggs then mix in butter, maple syrup and vanilla until well combined.
Mash banana. Add banana and yoghurt and mix until combined. Sift in flour, baking soda and baking powder. Add salt and walnuts and mix until just combined, careful not to over-mix. Transfer mixture to loaf tin.
Bake banana bread for 45-55 minutes, until golden and an inserted skewer comes out clean. Allow to cool in tin for 10 minutes, then remove from tin and cool on cooling rack until completely cooled. Store in an airtight container for up to 5 days.