Preheat the oven to 400˚F.
Bring the water and 1 of teaspoon salt to a boil in a heavy saucepan. Whisk in the polenta. Bring the polenta back to a boil, whisking constantly, then reduce the heat to low. Cover and cook 30-35 minutes, stirring every 10 minutes, or until the polenta is tender and creamy. Cover and keep warm.
In the meantime, place the sausages in a 13x9-in baking dish and pour in a quarter-inch of water. Cover tightly with foil. Bake 15 minutes. Transfer the sausages to a plate, pour off the water (save it to season a soup!), then put the onions, peppers, garlic, dried oregano, red pepper flakes and olive oil into the pan. Season with salt and pepper and toss everything around to coat. Place the sausages on top of the vegetables and bake (uncovered) 10 minutes. Increase the oven temperature to 450˚F. Flip the sausages over, give the vegetables a little stir, and arrange the tomatoes around the sausages. Bake 10-15 minutes longer, or until the sausages are lightly browned on top and the tomatoes begin to pop. Transfer the sausages to a cutting board. Squeeze the juice of ½ lemon over the vegetables. Taste and season with salt and pepper, if needed.
To finish the polenta, stir in the butter and the grated Parmesan cheese (feel free to eyeball it—a nice pile will do!). Taste and season with salt and pepper.
Slice the sausages on the diagonal. Spoon the polenta onto plates or into shallow bowls. Arrange the sausage slices on the polenta, then pile the vegetables on top. Using a vegetable peeler, shave some Parmesan over each. If you want, garnish with a bit of basil. Serve it up!