Heat 2 tbsp olive oil in a large casserole pan, then add the onions and cook for 8-10 minutes until translucent and starting to brown.
Add the garlic and cook for 1 minute, then tip in the aubergine and fry for 10 minutes until starting to soften and caramelise.
Stir in the stock paste, cumin and harissa, and cook for 1 minute before adding the chopped tomatoes, half a can of water and some seasoning. Bring to a simmer and cook for 10-15 minutes, until the sauce is reduced and the aubergine is cooked through.
Meanwhile, heat the grill to high. Drizzle the remaining olive oil over the pitta bread triangles and lay them on a baking tray. Grill for 2 minutes on each side, until golden and crisp.
Mix the yoghurt, with paprika, lemon juice, salt and pepper.
Check the stew for seasoning and serve with a dollop of yoghurt, fresh parsley and pitta chips.