Preheat oven to 325 degrees. Butter and flour metal loaf pan, set aside. In a medium bowl, whisk the flour with the baking powder, baking soda, and salt. In a large mixing bowl, mix the stevia with the eggs, vegetable oil and yogurt. Add the dry ingredients to the wet ingredients, along with the grated zucchini and walnuts. Stir until the batter is evenly moistened.
As a side note, make sure to buy the baking blend stevia. It can be found under the brand name Truvia in the grocery store. Enjoy!