Whisk the water, non-dairy milk, cornmeal, salt, and seasoning in a saucepan and bring to a boil. Reduce heat to low and continue to cook, constantly stirring, until it becomes thick, like a heavy oatmeal.
Pour the mixture into the casserole dish, spreading out evenly and patting down firmly but gently using a spatula. Cover and refrigerate until it sets, about an hour. Preheat oven to 450 F.
Remove covering and bake polenta completely uncovered for 25 minutes.
Remove and add a thin layer of sauce and your toppings. Careful not to use too much sauce or it will be soggy.
Bake another 10-15 minutes, until vegetables are cooked but still crisp and polenta is crisp along the edges.
