Preheat the broiler. Heat the olive oil in a large nonstick ovenproof skillet over medium-high heat. Add the polenta and fry until golden, about 3 minutes per side. Transfer to a plate.
Add the sausage to the skillet and cook, stirring and breaking it up with a wooden spoon, until just browned, about 3 minutes. Add the mushrooms and cook, stirring occasionally, until they soften, about 3 minutes. Add the garlic and cook 1 minute. Stir in the tomatoes, 1 teaspoon salt and 1/2 teaspoon pepper and bring to a boil. Reduce the heat to medium low and simmer until slightly thickened, about 5 minutes. Stir in the parsley.
Arrange the polenta rounds in the skillet on top of the sauce. Place the mozzarella slices over the polenta and sprinkle with the parmesan. Broil until the cheese is browned and bubbling, about 3 minutes. Top with more parsley and pepper to taste.
Feel free to use scallions instead of fresh parsley.
Courtesy of Food Network Magazine, Photograph by Andrew Purcell