While the spaghetti squash is baking, prepare the sauce.
Place the chopped pancetta in a large deep pan over medium-high heat. Fry until crispy, about 10-15 minutes.
Once cooked, remove the pancetta with a slotted spoon, keeping the grease in the pan. Set aside.
Add butter to the pan and add minced garlic. Cook until fragrant, about 1-2 minutes.
Add chopped mushrooms and fresh parsley. Cook until the mushroomed are browned, about 5 minutes. Season with salt and pepper.
Add frozen peas and cook for another 3-5 minutes.
Add white wine. Cook until the smell of the alcohol is gone and the liquid is halfway reduced.
Stir in the heavy cream, chicken broth, half the Parmigiano-Reggiano and all of the mozarella cheese. Bring to a simmer.
If the sauce is not thick enough, whisk in optional xanthan gum and continue simmering for another 3 minutes.
Adjust seasoning if needed.