1. In a deep bowl, beat the eggs. Add the milk and oil and mix well until the mixture is smooth.
2. In another bowl, mix the flour, salt, and baking powder. Gradually add the dry mixture to the wet mixture, stirring until you have a smooth dough.
3. Preheat the oven to 180°C. Prepare the cake tin by greasing it with oil and sprinkling it with a little flour.
4. Pour half of the cake mixture into the cake tin. Evenly distribute the thinly sliced onions, tomatoes, and sausage of your choice, then add the remaining cake mixture. Again arrange the thinly sliced onions, tomatoes, and sausage of your choice, then add the grated cheese, distributing it evenly.
5. Bake in a preheated oven at 180°C for 40 minutes or until the cake is golden and firm in the center. Check with a toothpick; if it comes out dry, the cake is done.
6. Remove the cake from the oven and let it cool for 10-15 minutes before removing it from the pan. Cut into pieces and serve warm or cold.