Best of both worlds: Leftover creamy polenta from tonight turns into crisp pan-fried polenta cakes tomorrow. Portobellos add meatiness and depth to this vegetarian dish.
Preheat oven to 400 degrees. Lightly coat an 8-inch square baking dish with cooking spray and set aside. In a medium pot, bring 10 cups water to a boil over high. Slowly add polenta, whisking constantly. Continue whisking until thickened, about 2 minutes; season with salt and pepper. Reduce heat to low and simmer, whisking occasionally, until polenta is thick and creamy, about 20 minutes. Pour half the polenta into baking dish and let cool; cover and refrigerate for Friday.
Meanwhile, place mushrooms, stem side up, on a rimmed baking sheet. Drizzle each with 1 teaspoon oil and season with salt and pepper. Roast 9 minutes. In a small bowl, toss together snap peas and 2 teaspoons oil; season with salt and pepper. Add snap peas to sheet with mushrooms and roast until snap peas are crisp-tender and mushrooms are tender and beginning to release their juices, 8 minutes.
Divide polenta among 4 plates and top each with a mushroom, some snap peas, and a sprinkling of Parmesan.