Preheat oven to 170 C / Gas 3. Spray a baking tray with a thin layer of cooking oil. Place squash halves cut side down on the baking tray.
Bake squash 35 minutes in the preheated oven or until a knife can be easily inserted. Remove from oven and cool.
Meanwhile, spray a non-stick saucepan with cooking spray. Over medium heat, saute the onion and garlic until golden brown. Stir in tomatoes, basil, stock cube and black pepper. Cook for about 15 minutes or until you have a medium thick sauce.
Remove squash strands with a fork, reserving the shells. Layer each half with a spoonful of the sauce, a layer of spaghetti squash strands, olives and mozzarella cheese. Repeat layers until shells are full or until all of the ingredients are used. Top with Parmesan cheese.
Bake for 20 minutes in the preheated oven or until Parmesan cheese melts.
Is also known as spaghetti marrow. They can be found in speciality markets.
Parmesan cheese is not truly vegetarian, as it contains animal rennet. To make this dish 100% vegetarian, omit the cheese or find a suitable vegetarian substitute made without animal rennet. In supermarkets look for the 'parmesan style hard cheeses' which are suitable for vegetarians.