Preheat the oven to 375 degrees.
Place the spaghetti squash halves cut side down in a rectangular baking dish. Add water to come up 1 inch in the pan.
Bake for 40 minutes or until squash is tender.
Using a fork, remove most of the flesh of the squash, leaving the shells behind.
In a large pan heat the olive oil over medium-high heat. Place the turkey sausage in the pan and cook, breaking up the meat with a spatula, for 5-7 minutes or until cooked through.
Add the marinara sauce and spaghetti squash into the pan; season to taste with salt and pepper and stir to combine.
Cook for 3-5 minutes, stirring occasionally until the sauce is warmed through.
Preheat the broiler. Divide the spaghetti squash mixture between the two shells and sprinkle the cheese over the tops.
Broil for 3-5 minutes or until cheese is melted and browned. Watch carefully so that it doesn't burn!
Sprinkle with chopped parsley and serve.