In a large mixing bowl, cream butter and sugar. Beat in egg and lemon juice until light and fluffy. Stir in sifted flour, baking powder, and salt until smooth.

Stir in zucchini and walnuts. Drop by rounded teaspoonfuls on greased cookie sheet. Bake in a pre-heated 375-F degree oven for 15 to 20 minutes.

Meanwhile, prepare icing by combining lemon juice and confectioners sugar in a small bowl, stirring to blend. Remove from cookie sheet to cool on a wire rack and drizzle lightly with icing while the cookies are still warm. Store in an airtight container for up to a week.