Preheat oven to 350F degrees.
Butter a 9"x5" loaf pan and then dust with flour (I used dark non-stick pan)
In a medium bowl, stir together 1 ¼ cup flour,1 teaspoon baking soda, ¼ teaspoon cinnamon, and ½ teaspoon salt.
In the bowl of a stand mixer, mix ½ cup brown sugar, ½ cup granulated sugar, 2 eggs, ½ cup coconut oil, 1 cup mashed bananas for about 3 minutes on medium speed to fully incorporate and smooth as much as possible. Turn mixer to low and add 1 cup grated zucchini, 1 cup grated carrots, ¼ cup sour cream (or yogurt), and 2 teaspoons vanilla.
Fold in flour mixture and just mix until combined. Using a rubber spoon, add ½ cup walnuts and scrape down the pan.
Pour the batter into prepared pan.
Bake on middle rack for 50-60 minutes (50 was PERFECT) until toothpick comes out clean.
Remove from oven to cooling rack. Cool about 10 minutes before removing from pan, then cool completely before cutting.