If using buttermilk, pour 1 tablespoon vinegar or lemon juice in a glass measuring cup and add enough milk to come up to the 1 cup mark. Let stand for 5 minutes.
In a large bowl, combine wheat flour, oats, ground flax, baking soda, cinnamon, and salt and stir with a whisk. Stir in raisins, cranberries, and dates. Make a well in the center of the mixture.
In a separate bowl, whisk the egg gently. Add the buttermilk mixture, honey, and vanilla and whisk again. Pour this mixture into the well in the center of the dry ingredients and stir just until moist. Stir in boiling water and let batter stand for 15 minutes.
Preheat oven to 375°F. Spoon batter into greased muffin cups. Bake for 20 minutes or until toothpick inserted in center comes out clean. Remove muffins from pan and cool on a wire rack. Enjoy!