Prepare sweet potato: Roast (200 °C / 400 °F, 40–50 min) or steam sweet potato until tender. Cool, peel, and mash until smooth.
Preheat oven: Set to 175 °C / 350 °F. Grease or line a loaf pan.
Combine wet ingredients: In a large bowl, whisk mashed sweet potato with miso until smooth. Add melted butter, sugar, and eggs, whisking until blended.
Mix dry ingredients: In another bowl, whisk flour, baking soda, baking powder, cinnamon, nutmeg, and salt.
Combine wet and dry: Gently fold dry ingredients into wet mixture until just combined—don’t overmix.
Add seeds: Fold in sesame, pumpkin, and sunflower seeds, reserving some for topping.
Fill and top: Pour batter into the pan, smooth the top, and sprinkle remaining seeds evenly.
Bake: Bake 50–60 minutes, or until a toothpick inserted in the center comes out clean.
Cool: Let cool 10 minutes in the pan, then transfer to a rack to cool completely before slicing.