Add the polenta in the boiled bouillon and boil for 3 minutes. Lower the heat and let simmer for 20 minutes more. Dice the pepper in cubes and the zucchini into strips. Fry chopped onions, add garlic, peppers, zucchini and spices, and let it simmer for 3 minutes, stirring constantly. Mix the cheese, lemon zest and spices. Pour and level the polenta on a greased pan. Put the vegetables on the top and bake in the oven for about 20 minutes at 200ºC. Cut and serve like a pizza.