1cupmarinara sauce,no added sugar (Rao's is a great brand)
Heat oven to 400 degrees F.
Using a large, sharp knife, cut the squash in half lengthwise: place it on a sturdy cutting board, slice off the stem end of the squash, then stand the squash upright on this flat end and carefully use your knife to slice it in half.
Using a spoon, remove the seeds and pulp.
Place the squash halves, cut side down, in a 9 X 13 baking dish. Add enough water to come 1/2 inch up the sides of the baking dish. Cover tightly with foil and bake 45 minutes. Turn over (careful - the whole thing will be very hot), cover again and cook 15 more minutes, until very tender. Remove onto a cutting board and allow to slightly cool.
Rake a fork back and forth across the squash to remove its flesh in strands. Divide among four plates. Pour the tomato sauce on top and sprinkle with the Parmesan. Don't pre-mix the sauce into the strands - this will result in soggy "noodles." Allow each diner to mix the sauce and cheese into their own spaghetti squash noodles.