Slice the aubergine in half lengthways, and hollow out the halves leaving about a 1cm shell. Set the flesh from the insides aside for later use. Place the shells on a baking tray, and drizzle with a little olive oil. Bake for about 30 minutes in the preheated oven, until soft.
While aubergine is baking, chop the leftover aubergine into small pieces. Heat about 2 tablespoons of olive oil in a large frying pan over medium heat. Add the onion and garlic; cook and stir for a few minutes. Add the chopped aubergine; cook and stir until tender. Mix in the tomatoes and tomato puree until well blended. Simmer over low heat until the halves in the oven are ready.
Remove the baked aubergine shells from the oven, and spoon in the tomato and eggplant mixture. Sprinkle a little cinnamon over the top of each one, and return them to the oven. Bake for another 30 minutes or so.