For the polenta zucchini casserole, bring the water to a boil. Add the salt and stir in the cornmeal. Let the polenta simmer for 10 minutes. Stir frequently.
Allow to cool and pour into a greased casserole dish. Preheat the oven to 180 degrees. Sauté the onion, then sauté the vegetables (zucchini, tomato) with the ham for about 5 minutes.
Deglaze with crème fraîche and season to taste. Put steamed vegetables on the polenta base and put processed cheese on top. Bake everything for about 25 minutes.