Preheat oven to 375F. Cut squash in half lengthwise, deseed, and remove any visible strings. Place the two halves cut side down on a baking sheet. Bake for 45 minutes or until soft (cooking time will depend on the size of your squash).
In the meanwhile, prepare the sauce. Heat oil in a large sauce pan over med-high heat. Add the onions and garlic and saute until soft, about 5 minutes. Add tomato paste. Add the tomatoes, breaking them upas you go. Bring the sauce to a boil, stirring often. Lower heat and simmer until sauce thickens, about 30 minutes. Season with Italian seasoning, salt and pepper.
Make the meatballs: Add all the ingredients in a large bowl and mix until well-combined. Shape into 18-20 golf-sized balls. Bake at 400F for 20 minutes.