Preheat oven to 190C (375F). Line a parchment paper on the bottom of a 23cm (9-inch) round baking pan. Set aside.
Make the filling: in a large skillet, heat olive oil over medium heat. Add chopped onion and sauté until lightly golden, about 6-7 minutes. Add grated carrot, diced bell pepper and cook, stirring frequently, for about 5-7 minutes. Add sliced cabbage and cook for 10-12 minutes.
Turn the heat off and set aside.
In a bowl mix mayonnaise, sugar, salt, baking powder and 3 tablespoons of flour. Mix until smooth. Add eggs and mix until combined and smooth. Add the rest of the flour and mix until smooth and a bit thick (as shown in the video).
Pour half of the batter to the bottom of the baking pan and spread evenly. Then, spread the filling over the batter, then pour the rest of the batter on top of the filling and spread evenly.
Sprinkle some white sesame seeds/black sesame seeds/nigella seeds (optional).
Bake for 25-30 minutes or until golden brown on top.
Allow to cool for at least 20-30 minutes, then release from the pan and serve.