Preheat the oven to 180 C / Gas mark 4. Butter and flour a large loaf tin.
Whisk together flours, oats, bicarb, cinnamon and salt.
Stir together yoghurt and honey in a large bowl; beat in eggs and vanilla. Alternate adding flour mixture and bananas 4 times, scrapping down sides and mixing just until incorporated. Fold in carrots, sultanas and seeds. Spoon into prepared tin; sprinkle the top with additional sunflower seeds.
Bake in the preheated oven until a skewer inserted into the centre comes out clean, 55 to 60 minutes. Cool for 15 minutes in the tin then remove and finish cooling on a wire rack.