Preheat oven to 220°C (200°C fan-forced). Preheat a large, heavy rimmed baking tray on a rack in lower third of oven. In a bowl, toss carrots and onion with 2 tbs of the oil and season with salt and pepper.
Add the carrots and onion to the tray and roast, shaking the tray occasionally, for 20-25 mins or until vegetables are browned and tender.
Meanwhile, in a saucepan, bring honey, vinegar and 1 tbs of remaining oil to the boil over medium heat. Season. Transfer to a bowl and set aside to cool.
Place the couscous in a medium heatproof bowl. In the saucepan, bring 11/2 cups (375ml) water, the sultanas, 1 tbs of the remaining oil and 1/2 tsp salt to the boil over high heat. Pour over couscous, stir once and cover bowl tightly with plastic wrap. Set aside for 10 mins. Uncover and fluff couscous with a fork. Stir in 2 tbs of the dressing, half the walnuts and half the spring onions. Season. Transfer to a platter.
Heat remaining 1 tbs oil in a large non-stick frying pan over medium-high heat. Cook haloumi for 2 mins each side or until golden and crisp.
Top couscous with vegetables and haloumi. Drizzle remaining dressing over vegetables. Sprinkle with dill, parsley, mint, remaining walnuts and remaining spring onions.