Preheat oven to 375 degrees Fahrenheit and line a baking sheet with parchment paper.
Cook your spaghetti squash. Using a sharp knife, cut your spaghetti squash in half lengthwise and remove the seeds. Drizzle the flesh of the spaghetti squash with a little olive oil and a sprinkle of salt and pepper. Place cut side down on the baking sheet and roast for 35-40 minutes until tender and the skin gives a little when touched.
Brown your chicken. When the spaghetti squash has about 10 minutes left, make the chicken. Heat a large skillet over medium heat. Add oil and let it get hot. Then add the chicken and garlic and cook for 5-6 minutes stirring occasionally, until browned on the outside (it will continue to cook as you go). Next, add Italian seasoning, salt, and pepper and stir to coat. If there is a lot of liquid in the pan, remove some of it as it will water down the sauce.
Add pasta sauce and parmesan cheese and mix to combine.
When spaghetti squash is done, remove it from the oven and thread flesh with a fork to make spaghetti. Be careful not to break the skin of the squash.
Assemble. Divide the ground chicken among the 4 halves, making sure to get the sauce and juices. Evenly distribute the mozzarella cheese over the chicken mixture. Place back in the oven for 5-10 minutes until cheese is melted. If desired, you can place it under the broiler for 2-5 minutes, watching carefully to make sure the cheese doesn’t burn.
Enjoy! Garnish with optional toppings and enjoy!