Warm up your oven to 425°F (218°C) and line a baking sheet with foil or parchment paper for easy cleanup.
Carefully poke the spaghetti squash all over with a sharp knife. Place it on the prepared baking sheet and roast for 30-45 minutes, turning it over halfway, until it feels tender when you gently pierce it with a knife.
Take the squash out of the oven and let it cool. Increase your oven temperature to 450°F (232°C) to get ready for the chicken.
Once cool enough to handle, slice the squash in half, scoop out the seeds, and use a fork to easily pull out the spaghetti-like strands. Season these lovely strands with a pinch of salt.
Arrange the chicken breasts in a baking dish, making sure they aren't crowded. Brush both sides of the chicken with melted butter.
Sprinkle generously with Italian seasoning, garlic powder, sea salt, and black pepper on both sides.
Bake for about 18-22 minutes, or until the chicken's internal temperature reaches 160-165°F (71-74°C). (It will finish cooking as it rests!)
Cover the chicken with foil and let it rest for 5 minutes, then cut it into bite-sized pieces.
While the chicken is baking, melt 1 tablespoon of butter in a large saucepan over medium heat. Add the minced garlic and sauté for about 1 minute until it smells wonderful.
Pour in the heavy cream and bring it to a gentle simmer. Cook for about 5 minutes, stirring often, until the cream has thickened slightly (reduced by about 1/3).
Lower the heat to low. Gradually whisk in the grated Parmesan cheese until it melts smoothly into a creamy sauce.
Stir in the nutmeg, sea salt, and black pepper to your liking. If the sauce feels too thick, simply add a splash more cream to thin it out.
In a large bowl, combine your tender spaghetti squash noodles with the creamy Alfredo sauce. Toss gently to make sure everything is well coated. Give it a taste and adjust any seasonings if needed.
Add the cooked chicken pieces to the bowl and toss again.
Finish your delicious Spaghetti Squash Alfredo with a sprinkle of fresh parsley for a burst of color and flavor!