Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13 inch pan.
In a large bowl, mix together the eggs, oil, sugar and vanilla until well blended. Combine the flour, baking powder, baking soda and salt; stir into the sugar mixture. Mix in the zucchini. Spread the batter evenly into the prepared pan.
Bake for 20 to 25 minutes in the preheated oven, until a toothpick inserted into the center comes out clean. Allow bars to cool completely before frosting. To make the frosting, blend together the margarine, cream cheese and confectioners' sugar until well blended. Spread over cooled bars before cutting.