Cut zucchini in half, then cut in half again. Slice in diagonal pieces. Add to large bowl. Dice plum tomatoes. Add to zucchini in bowl. Add sliced mushrooms and 1/2 the sliced green onions saving 1/2 for topping. Set aside.
Remove wrapper from polenta tube and slice into 1/4 inch slices. Add your favorite marinara or tomato sauce to large saucepan, heating to medium, but do not boil. In large skillet heat olive oil to medium high. Add polenta slices to skillet, not over crowding. Saute on both sides till lightly browned. Set first batch aside on warmed plate and place in 200 degree oven to keep warm.
Add all the vegetables to tomato sauce, turn heat down to medium-low. Stir occasionally. Add salt and pepper, and Italian Seasoning. You want to heat the vegetables, not cook them. Taste for possible addition of more salt and pepper or Italian seasoning and be sure they are heated through. Finish sauteing the polenta. Remove heated plate of polenta from oven, and add this batch to it.
Depending on how many polenta slices you have, measure out on 4 plates. Top with large spoonful of vegetable mixture. Top that with the remaining green onions and the chopped cilantro, measured out for 4 plates. Sprinkle Parmesan cheese over all.
We like this with a salad and crusty bread for accompaniment.