Preheat the oven to 375°F. Grease or line two medium loaf pans (either 81/2 × 5 × 2¾-inch or 71/2 × 4 × 2-inch) with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. Set aside.
In a large bowl, whisk the eggs well. Add the sugar, oil, andvanilla extract; whisk well. Add the shredded zucchini, walnuts,and dry ingredients to the bowl. Stir with a woodenspoon until combined. Divide the batter between the two prepared pans.
Bake in the middle of the oven for 45–50 minutes, until the tops are browned and a toothpick inserted into the centers comes out clean. Remove from the oven. Let cool completely. Add the 3 tea bags to the boiling water and let steep for 3 minutes. Remove the tea bags and chill the tea in the refrigerator several hours until cold.
For the glaze: Sift the confectioners’ sugar into a small bowlwith the salt. Start by adding 1 tablespoon of the cold tea tothe sugar mixture and whisk well. Dribble up to 1 tablespoonmore tea as needed, whisking all the while. The icing should be loose enough to drizzle, but thick enough to coat the cake without running off. If it’s too thin, sift in another tablespoon of confectioners’ sugar. If it’s too thick, add more tea a few drops at a time. Freeze the remaining tea for future use.
Pour or drizzle the glaze over the top of the cake. Sprinkle with finely chopped walnuts, if desired. Let sit in the refrigerator for 15 minutes to set.
Serve at room temperature. Leftovers can be covered and stored in the refrigerator for 4–5 days.