Preheat the oven to 200°C, fan 180°C, gas 6. Put the aubergine halves, cut side up, on a baking tray and cook for 40 minutes. Cool slightly, then scoop out most of the cooked flesh (reserve for later), leaving the skin and a layer of flesh intact.
Meanwhile, heat 1 tablespoon of the oil in a large pan. Add the onion and cook for 5 minutes, stirring in the garlic, cumin and oregano for the final minute. Stir in the lamb mince and cook for 3-4 minutes, then add the chopped tomatoes. Cook for 10-15 minutes over a medium heat, then stir in the cherry tomatoes and season with freshly ground black pepper.
Preheat the grill to high. Roughly chop the reserved aubergine flesh and stir into the lamb mixture with half the potatoes. Spoon the mixture into the aubergine halves and top with half the cheese. Mix the remaining potatoes and cheese with oil and put on the baking tray next to the aubergines. Grill for 5 minutes, until the cheese is melted and golden.
Meanwhile, put the spinach in a pan over a medium heat with a splash of water. Cover and wilt for 2-3 minutes, stirring occasionally. Serve with the aubergines and potatoes.