Place squash halves cut side down onto a plate. Cook the squash in a microwave oven for 5 minutes on High, until tender but firm.
In a medium skillet over medium heat, cook sausage and onion until evenly browned, season to taste; drain, and set aside.
In a large bowl, mix together the rice, sausage, and mozzarella. Stuff each squash half with the mixture.
Cover stuffed squash halves with plastic wrap, and heat in the microwave until squash is cooked through and soft, about 5 minutes. Remove plastic, and top stuffed squash with parmasan cheese (I added a little more mozzarella too.) Continue to cook about 1 minute.
This makes a fabulous meal all in one neat little package! There are things that could be done to make it a little better for you...like using turkey sausage, but I couldn't find any at the store, so I haven't tried that yet. Anyway, I just wanted to share! Hope you enjoy!