For the polenta casserole, add polenta to salted boiling water and simmer, stirring until the mixture separates from the bottom of the pot.
Sauté the onion in oil, add the cleaned, chopped vegetables and continue to saute.
Let the vegetable mixture cool down a bit with the polenta mixture, mix it and add half of the cheese and the eggs.
Pour the mixture into a baking dish, sprinkle with the remaining cheese and bake for about half an hour.