Preheat oven to 325º F. Start by finely grating the orange rind. In a large bowl combine baking soda and salt to the flour, and mix thoroughly. Add sugar and stir. Add the orange rind to the dry ingredients.
In a separate bowl, whisk together the egg, vinegar/water mixture, orange juice, and oil. Make a well in dry ingredients, and pour wet ingredients in all at once, stir quickly just until moistened. Fold in cranberries and walnuts (if using).
Pour into a greased 9 x 5-inch loaf pan and bake until golden brown and toothpick inserted into the center of the loaf comes out clean (approx. 60 minutes). Cool in the pan for 10 minutes, then turn the loaf out onto a wire rack to cool completely. Slice, and enjoy!
