Preheat your oven to 350°F (175°C) and grease a 9x5-inch loaf pan.

In a light-colored saucepan, brown 6 tablespoons of butter over medium heat for about 5-7 minutes.

Grate 1 medium zucchini, then squeeze out excess moisture using a kitchen towel.

In a bowl, mix granulated sugar with cooled brown butter, then add 2 eggs and 1 teaspoon lemon juice.

In another bowl, whisk together flour, baking powder, salt, cinnamon, and lemon zest.

Gently fold dry ingredients into the wet mixture until just combined.

Prepare the walnut streusel by mixing walnuts, brown sugar, cinnamon, and salt in a bowl.

Pour the batter into the prepared pan and sprinkle the streusel on top. Bake for 50-60 minutes.

Cool the loaf in the pan for about 10 minutes, then transfer to a wire rack to cool completely.