Prep: Preheat your oven to 325°F (165°C). Take two 8×4-inch loaf pans and grease them well with butter or cooking spray, then lightly dust the insides with flour. Tap out excess flour. This prevents sticking.

Mix dry ingredients: In a large mixing bowl, combine 3 cups all-purpose flour, 1 teaspoon salt, 1 teaspoon baking powder, 1 teaspoon baking soda, and 1 tablespoon ground cinnamon. Use a whisk to blend everything evenly for 30 seconds until no streaks of cinnamon remain. Checkpoint: Your dry mixture should look evenly colored with no visible clumps of baking soda or powder.

Beat wet ingredients: In a second large bowl, add 3 large eggs, 1 cup vegetable oil, 2¼ cups granulated sugar, and 3 teaspoons vanilla extract. Using an electric mixer on medium speed, beat for 2–3 minutes until the mixture is pale, smooth, and slightly thickened. You should see pale ribbons when you lift the beaters. Checkpoint: The mixture should look creamy and uniform with no visible egg whites.

Combine wet and dry: Pour the wet ingredients into the dry ingredients. Using the electric mixer on low speed (or a rubber spatula), mix for 1–2 minutes until just combined. Do not overmix—a few small flour streaks are fine. Overmixing makes the bread tough. Checkpoint: No large streaks of flour remain, but the batter looks slightly lumpy.

Add zucchini and walnuts: Using a rubber spatula, gently fold in 2 cups shredded zucchini (freshly shredded or patted dry to remove excess water) for 30 seconds until distributed. Then fold in 1 cup chopped walnuts for another 30 seconds, stirring until even. Do not overwork. Checkpoint: You can see flecks of green zucchini and brown walnut pieces throughout the batter without any large pockets.

Fill pans: Divide the batter evenly between the two prepared loaf pans using a rubber spatula or spoon. Gently smooth the tops. Fill each pan about two-thirds full. Checkpoint: Both pans have roughly equal amounts of batter, and the surfaces are relatively level.

Bake: Place both loaf pans on the middle oven rack. Bake for 40–60 minutes until a toothpick inserted into the center of each loaf comes out clean (no wet batter clinging to it—a few moist crumbs are okay). The tops should be golden brown and a toothpick should meet slight resistance. Checkpoint: Toothpick comes out mostly clean, tops are deep golden brown, and the bread has risen above the pan edges.

Cool in pans: Remove the pans from the oven and place on a wire cooling rack. Let the loaves rest in the pans for 20 minutes. This allows them to set and firm up enough to handle. During this time, the bread will cool slightly but still be warm.

Release from pans: Run a thin knife (like a butter knife) around the inside edges of each loaf pan, gently sliding it between the bread and the pan to loosen it. Do this carefully to avoid breaking the bread. Tip each loaf out onto your hand or a small plate, then transfer it to a wire cooling rack top-side up.

Cool completely: Let the loaves rest on the wire rack at room temperature for at least 1–2 hours (or until completely cool to the touch). This is important—cutting into warm bread can cause it to crumble. Once cool, the crumb will set and hold together better when sliced. Checkpoint: The loaf feels cool and firm to the touch, and you can slice it cleanly without it tearing.