In a large skillet, start browning ground beef and Italian sausage on medium-high heat, breaking meat into smaller pieces with wooden spoon. Drain excess fat.
Add in salt, pepper, garlic powder, red pepper flakes and stir until meat is cooked through.
Add in tomato paste and vegetable stock and mix until evenly incorporated.
Preheat oven to 375 degrees F.
Add in tomato puree, sweetener, dried oregano and basil. Let cook and stir occasionally for about 10 minutes.
Add in spaghetti squash and stir until incorporated.
In a medium sized casserole dish, spread out half of the mixture on the bottom of the pan.
On top, layer the mozzarella, parmesan and half of the pepperoni.
Add remaining squash and meat mixture on top.
Top with remaining pepperoni and reserved mozzarella.
Cover with foil and place into oven for 45 minutes.
Take out of oven and remove foil.
Change oven temperature to broil.
Place back into oven until cheese is bubbly and golden brown. Usually 2-5 minutes.
Remove from oven and let rest for at least 10 minutes.