Preheat the oven to 400 degrees. Grease a 12 cup muffin tray.
Place cranberries in a 1 cup measuring cup and cover with warm water. Let sit for 10 minutes then drain and squeeze excess water out with a paper towel.
Meanwhile, whisk together the flour, sugar, baking powder, salt, and lemon zest in a medium sized bowl. Stir in the walnuts and cranberries.
In a small bowl whisk together the eggs, milk, and oil. Make a well in the center of the flour mixture and pour the wet ingredients in. Use a wooden spoon to gently stir the batter until barely combined. Gently fold in the zucchini.
Spoon batter into muffin cups--you'll fill them nearly to the top. Bake for 20-25 minutes or until tops spring back when touched. Remove from the oven, cool for 5-10 minutes, then turn out of the pan to finish cooling.