Preheat the oven to 180°C(fan)/200°C/gas mark 6. Line a muffin tin with 18 fairy cake cases or 12 muffin cases.
Place the oats in a food processor or blender and grind to a powder.
Place 250g plain flour, 1.5 tsp baking powder, 3/4 tsp bicarbonate of soda, 1 tsp ground ginger, 1/2 tsp grated nutmeg and 1.5 tsp ground cinnamon into a bowl and whisk together until well combined. Add up to 200g caster sugar if desired (see note above about sugar). Set aside.
Whisk together the 180ml sunflower oil, 120ml milk, 1.5 tsp vanilla extract and 1 tbsp lemon juice. Stir in 2 mashed bananas. Set aside.
Peel and grate 200g parsnips and 1 large apple.
Gently fold the oil and milk mixture into the flour mixture. Add the grated parsnip and apple into the flour mixture, stirring until just combined. Finally stir through the 100g raisins or sultanas.
Spoon the batter into your muffin cases and bake for 20 to 25 minutes until deep golden brown and a toothpick inserted in the centre of a muffin comes out clean. Cool muffins on a wire rack.
Store in an airtight container for 2-3 days or freeze.