Preheat the oven to 180°C. Line a muffin tin with paper cases or use silicone cases.
Coarsely grate the beetroot and carrots.
In a large bowl, mix the grated vegetables with the mashed banana, eggs, oil and sugar.
If the mixture feels very coarse, briefly blend with a hand-held blender until you get a rough purée.
In a separate bowl, mix the flour, baking powder and cinnamon.
Fold the dry ingredients into the wet mixture. If the batter seems too thin, add a little more flour or oats – it should be thick but pourable.
Fold in the raisins or sultanas.
Spoon the batter into the prepared muffin cases.
Bake for 20–25 minutes, until risen and a skewer inserted into the centre comes out clean.
Transfer the muffins to a wire rack and allow to cool before serving.