In a large bowl whip eggs and sugar until light. Mix in the orange essence and oil. Combine the flour and baking powder; stir into the egg mixture along with the walnuts. Form dough into 4 logs and place them 8cm apart onto an ungreased baking tray; flatten slightly.
Bake in the preheated oven for 20 to 25 minutes or until golden and firm to the touch. Remove from the oven and cool completely. Remove to a cutting board and slice each log into 2cm wide diagonal slices with a serrated knife. Return the slices to the baking tray, cut side down.
Return the slices to the oven and bake for an additional 5 to 10 minutes, until toasted.