Preheat oven to 325 degrees F (165 degrees C). Grease and flour two 8x4-inch loaf pans.
Beat eggs until light and frothy in a large bowl. Mix in oil and sugar. Stir in zucchini and vanilla extract. Combine all-purpose flour (or gluten-free flour), buckwheat flour, cinnamon, baking soda, baking powder, salt, and nuts in a bowl. Stir flour mixture into egg mixture. Divide batter into prepared pans.
Bake in preheated oven until a toothpick inserted into the middle of the loaf comes out clean, 60 to 70 minutes.