Preheat oven to 350F and grease two 8x4" loaf pans. Set aside.
In a medium mixing bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment (or in a large mixing bowl with an electric hand mixer), combine sugar and vegetable oil. Mix well on medium-low speed to combine.
Add sour cream and mix to combine. Then add eggs, one at a time, mixing well after each addition and scraping down the sides of the bowl as needed.
Add vanilla extract, diced peaches, and shredded zucchini. Mix on low speed until incorporated.
With the mixer on low speed, gradually add the flour mixture to the bowl, scraping down the sides of the bowl as needed. Mix just until the dry ingredients are evenly incorporated into the batter.
Divide the batter between the two prepared loaf pans. Bake in preheated oven for about 55-60 minutes, or until a toothpick inserted in the center of the loaf comes out clean.
Remove from oven and let cool in the pans for about 10-15 minutes, then run a knife along the edges of the loaves and turn the loaves out onto a cooling rack to cool completely.