In a medium bowl, mix together flour, brown sugar, baking
powder, cinnamon, and salt. Mix in nuts.
In another bowl, combine zucchini, oil, eggs, and vanilla; add to
flour mixture, and mix just until combined (do not overmix).
Cool in tin on a wire rack for 10 minutes; turn cupcakes out, right
side up, and cool completely. Meanwhile, make frosting. Using a
offset spatula or butter knife, spread frosting on cupcakes.