Preheat oven to 350°F (175°C). Grease and line a 9×5-inch loaf pan with parchment paper for easy removal.

In a small bowl, mix brown sugar, flour, cinnamon, cardamom, and salt. Cut in the softened butter until crumbly; set aside.

Rinse your zucchini under cool water, then cut off both ends. Using the large holes of a box grater or the shredding disk of a food processor, grate the zucchini. No need to peel — the skin is thin and blends right into the batter. Place the shredded zucchini in a clean kitchen towel or a few layers of paper towels. Gently squeeze over the sink to remove excess liquid. You don’t want it bone-dry — just remove enough water so it won’t make your bread soggy. Always measure the zucchini after you’ve removed the moisture to ensure the correct amount for the recipe. Set aside.

In a large mixing bowl, cream together butter, granulated sugar, and brown sugar until fluffy (1–2 minutes). Whisk in eggs, oil, vanilla, and orange zest. Stir in the shredded zucchini and buttermilk.

In a separate bowl, whisk together flour, salt, baking powder, baking soda, cinnamon, and cardamom. Add to the wet mixture and stir just until combined.

Spread half the batter into the prepared pan. Evenly sprinkle all the streusel mixture over it. Spoon the remaining batter on top, smoothing gently.

Bake 50–55 minutes, or until a toothpick inserted in the center comes out clean. If the top browns too quickly, tent loosely with foil during the last 15 minutes.

Let bread cool in the pan for 10–15 minutes, then transfer to a wire rack. Cool completely before slicing for the best texture.