Preheat oven to 350°F. Line a muffin tray and lightly grease the liners or use silicone muffin liners.
In a large mixing bowl, combine pumpkin puree, sugar, walnut butter, vinegar, soy milk, and vanilla.
Mix in spices.
In a small bowl, whisk together whole wheat flour and baking soda. Add to wet ingredients and gently fold to combine into a cohesive batter.
Add nuts and gently fold a few more times to distribute. Be careful not to over-mix or your muffins will turn out dense.
Bake 25-27 minutes, until a toothpick inserted in the center comes out clean or with just a few crumbs (but no wet batter). Let muffins cool in the pan for 5 minutes, then carefully transfer each muffin to a wire rack to cool completely.
Store leftovers in an airtight container at room temperature for up to 2 days, in the fridge for 5 days, or in the freezer for about 2 months.