Place spaghetti squash in a large baking dish and bake at 400º for about an hour, to an hour and a half, or until cooked through.
Allow to cool.
Meanwhile, crumble ground beef and Italian sausage into a large Dutch oven.
Heat over medium heat, turning meat frequently until it is no longer pink.
Use a hamburger chopper to break the meat up into small pieces while frying.
Add onion, garlic, bell pepper and mushrooms.
Sauté a few minutes until vegetables are tender.
Add tomatoes, tomato paste, tomato puree (if using) and seasonings including the bay leaves.
Reduce heat to low; cover with lid and cook about 1 ½ hours or until bubbly and flavors have blended.
Cut spaghetti squash in half and remove pulp and seeds; discard.
Use a fork to remove the strands of spaghetti squash and place on a serving platter.
Keep warm.
Once sauce has cooked, remove bay leaves.
Serve sauce over hot, cooked spaghetti squash and garnish with Parmesan cheese.