Place the aubergine on a baking tray with a tablespoon of olive oil and a sprinkling of salt and pepper. Cook at 200°C for 20 minutes. Meanwhile place the couscous in a large bowl with 400ml of boiling water. Cover the bowl with a clean towel.
Heat the rest of the olive oil over a medium heat in a frying pan. Add the yellow pepper and red onion with a pinch of salt. Cook for 15 minutes. Remove the vegetables from the pan and place in the bowl with the couscous. Return the pan to the heat and fry the halloumi until browned on both sides, adding more oil if necessary.
To make the dressing mix together the harissa paste, vinegar, olive oil and sugar. Set aside. To finish assembling the salad add the aubergine, spinach, tomatoes and halloumi to the vegetables and couscous then toss with the dressing.