Line the bottom of a 9-inch by 9-inch baking pan with parchment paper or aluminum foil.
Liberally coat the paper or foil with oil spray.
In a large saucepan, combine 3 cups water and the salt.
Bring the water to a boil.
Slowly whisk in the polenta. Reduce the heat to low and cook for 30 minutes, or until the polenta is very thick, stirring every 5 to 10 minutes.
Stir in the cheese. Spread the polenta into the prepared baking pan, making it as smooth and even as possible.
Cool the polenta on the counter for 10 minutes. Lay a sheet of plastic wrap directly over the top of the polenta.
Refrigerate for at least 2 hours, but ideally overnight, to allow the polenta to firm up.
Preheat the oven to 425°F.
Line a baking sheet with parchment paper or aluminum foil.
Flip over the baking pan onto a cutting board to release the polenta in one square.
Remove the parchment paper or foil. Slice the polenta square in half, and slice each half into 8 to 10 strips (“fries”).
Arrange the polenta “fries” on the baking sheet. Bake the fries for 30 minutes, flipping once halfway through, until golden brown and crispy.
Optional: Serve with warm marinara sauce for dunking!