Beat the eggs and sugar with a mixer. Add the oil and cinnamon. Sift the flour and baking powder and them to the mixture.
Peel and grate the apples (don't do this beforehand because they'll darken). Grind the walnuts with the apples and add them to the mixture as well. Stir everything well.
Pour it into an oiled tray or cake form and bake in a 320°F (160 °C) oven to a dry toothpick.