Preheat the grill. When hot, grill the pepper until the skin is blackened on all sides. Put in a plastic bag to cool. Remove the skin, stalk and any seeds, and cut into 2cm strips.
Heat 2 tbsp of the oil in a large, thick-bottomed saucepan, add the onion and let it soften and colour. Add the garlic and chilli, and cook for 3-4 minutes.
Add the tomato and 1 tsp salt, and simmer gently for 35 minutes.
Boil the potato in a small saucepan of salted water until al dente. Drain. Meanwhile, in a separate large saucepan, heat 4 tbsp olive oil. When hot, add the aubergine cubes and brown all over. Cook until tender. Remove and drain.
In a separate bowl, combine the tomato sauce with the aubergine, potato and pepper. Sprinkle with the vinegar, salt and pepper, and stir together. Add the marjoram.
Serve drizzled with extra virgin olive oil, warm or at room temperature.