Preheat the oven to 190 C / Gas 5. Grease a baking dish.
Cut the aubergine in half lengthways and scoop out the flesh, leaving a shell 1.5cm thick. Sprinkle the aubergine halves and flesh with salt and set aside for 15 minutes.
After 15 minutes, rinse the aubergine halves and flesh. Pat dry, then chop the flesh.
In a frying pan, heat the oil and cook and stir the onion until translucent. Add the chopped aubergine, tomato, garlic and pepper and mix well. Season with paprika, oregano and salt and pepper and cook and stir for 5 minutes. Stir in the olives, reserving 2 tablespoons olives for garnish.
Spoon the filling into the aubergine halves and cover with mozzarella slices. Transfer to the prepared baking dish.
Bake in the preheated oven for 40 minutes. Remove from the oven and garnish with reserved olives before serving.