Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13 inch baking pan.
In a large bowl, beat the eggs and vegetable oil together until well blended. Combine the flour, sugar, cocoa powder, baking powder and salt; stir into the egg mixture. Fold in walnuts if desired. Spread evenly into the prepared pan.
Bake in the preheated oven for 20 to 25 minutes, or until a toothpick inserted into the center of the brownies comes out clean. Allow to cool. Cut into squares.