Pour the water and salt into a medium-size pot; bring water to a boil. Add the polenta and reduce heat to low; cover and cook, stirring occasionally, for about 5 minutes. Stir in the oil.
Oil the bottom and sides of an 8 x 8-inch casserole; spoon the polenta into the casserole and let sit for 10 minutes, or until firm. When firm, cut polenta into four squares and place on individual plates.