These muffins are healthy single-serving breakfast breads that verge right on the border of sweet and savory. If you want to take this recipe into a sweeter territory, add in some chocolate chips or raisins.
Preheat the oven to 350 degrees F. Line a 12-cup muffin tin with liners or spray with nonstick cooking spray.
In a medium bowl, whisk together the sugar, applesauce, yogurt, vanilla extract, and eggs. In a separate bowl, mix the flour, cinnamon, salt, baking powder, and baking soda. Mix the dry ingredients into the wet ingredients. Gently fold in the walnuts, chocolate chips if using, and zucchini.
Fill the cupcake liners almost all the way to the top. Bake the muffins until browned on top and cooked through, about 20 minutes. Cool the muffins in the pan, and serve.