Preheat oven to 175 degrees C. Line a 12-cup standard muffin tin with paper cases.
Place dates in a bowl; cover with soy milk. Let stand until softened, 10 to 15 minutes.
Mix water and flax seeds together in a separate bowl. Let stand until thickened, 5 to 10 minutes.
Combine oat flour, millet flour, tapioca flour, baking powder, cinnamon and bicarb in a bowl. Mix well.
Place the soy milk-date mixture, apples puree and vanilla extract in a blender or food processor. Blend until smooth. Transfer to the bowl with the flour mixture; add the soaked flax seeds. Mix with a spoon until no dry spots remain. Fold in apples, walnuts and raisins gently. Spoon batter into the muffin cups.
Bake in the preheated oven until a toothpick inserted into the centre comes out clean and tops begin to brown and form cracks, 30 to 35 minutes. Cool for 15 to 20 minutes before serving.