Preheat the oven to 220°C (fan 200°C/gas mark 7).
Score the white flesh of the aubergine halves in a criss-cross pattern, without cutting through the skin at the bottom. Spray the halves all over with low calorie cooking spray.
Lay the halves on a foil-lined baking tray, cut side up. Season with salt and pepper. Roast the halves in the middle of the oven for 30 minutes.
While the aubergine is cooking, spray a frying pan with low calorie cooking spray and place over a medium heat. Add the onions, pepper and garlic and sauté for 5 minutes, until the onion has softened.
Add the tomatoes, paprika, sumac, cinnamon, oregano, sweetener and balsamic vinegar. Season with salt and pepper and and simmer for 5 minutes until the mixture has thickened and deepened in colour.
Remove the aubergine halves from the oven. Carefully press down the edges of each aubergine so that the criss-cross sections open up more, creating channels for the sauce to seep into. Spoon the tomato mix on top and place the aubergines back in the oven for 10 minutes.
Remove from the oven and serve.