Bring water to boil in a high sided pot. Slowly add polenta to the pot and stir constantly until the polenta and water are mixed. Lower the heat to medium-low.
Add salt and ground thyme to the pot. Stir frequently for about 5 minutes, or until polenta starts pulling away from the pot.
Stir in the manchego cheese until melted.
Pour into a 8x8 inch baking dish (sprayed with cooking spray), spread with a wet or oil covered spatula, and refrigerate for 30-45 minutes.
Once the polenta has cooled and set, cut into 4 inch x 1/2 inch rectangles.
Preheat oven to 450F. Brush or toss the polenta fries with oil. Bake for 25 to 35 minutes, turning once, until golden and crisp. Drain on a paper towel lined plate.
Serve with marinara sauce for dipping.