Preheat oven at 350° F. Add 2 teaspoons apple cider vinegar to a half cup measuring cup and fill remainder of cup with vanilla soymilk, set aside. In a large mixing bowl, cream butter with agave nectar and avocado for a minute or two with a fork. Small bits of butter and avocado are fine.
In a separate bowl, combine the dry ingredients (all-purpose flour, whole wheat flour, salt, baking soda, and baking powder) and mix well. Add the wet ingredient mixture to the dry ingredients all at once, and stir just until just combined. Do not over-mix.
Divide the mixture in a 12-muffin pan that has been lined or coated with non-stick spray. Bake 20 minutes at 350° F until a toothpick inserted into a muffin center comes out clean.
After a couple of minutes, remove muffins from the pan. Prepare the glaze (recipe below) and pour glaze with a spoon over the slightly cooled muffins.