Combine the flours, baking soda, baking powder, cinnamon, ginger, nutmeg and salt together in a medium bowl. Mix until fully combined.
In a separate large bowl, add the eggs, oil, Greek yogurt, honey, cooked sweet potato, and vanilla extract. Using a hand mixer, beat the batter together until fully mixed. Stir in the dry ingredients and mix until just combined.
To make the walnut streusel, place the walnuts into the food processor. Pulse a few times to break the pistachios into smaller pieces. In a small bowl, combine the ground walnuts, brown sugar, flour, and pinch of salt. Add the melted butter and stir together.
Divide the muffin batter into 12 muffin tins with muffin liners. Evenly top each muffin with the walnut streusel. Bake for 5 minutes at 400 degrees, then reduce heat to 350 degrees for 11-14 minutes more or until the batter is set. Let cool and enjoy!