Preheat oven to 190 degrees C.
Combine flour and baking powder. Sift twice. Add lemon rind, nutmeg and bran. Mix well. Stir in currants. Beat egg whites until stiff. Add milk, yoghurt and zucchini. Pour into flour mixture and gently fold through. Lightly grease muffin tins and sprinkle with wholemeal flour or bran. Shake off excess. Spoon mixture into the muffin tins and bake for 25 minutes.