Heat your oven to 200°C/Fan 180°C/Gas 6. Peel the onions and chop each into 8 wedges. Chop the tomatoes into wedges similar in size to the onions. Trim the courgette and chop into chunks. Scatter all 3 ingredients into a large roasting tin.
Peel and finely chop the garlic. Halve the chilli, flicking out the seeds and white membrane for less heat, and finely chop. Scatter the chopped chilli and garlic over the veg, along with a good pinch of ras al hanut and a little salt and pepper. Pour over 1 tbsp oil and toss everything well to combine. Slide into the oven and roast for 20 mins till the veg are tender and a little charred.
Meanwhile, tip the couscous into a heatproof bowl and add a little salt. Pour over 300ml boiling water. Cover with a plate. Set aside for 15 mins to soak.
Rub the lamb steaks with a pinch of ras al hanut and some salt and pepper till evenly covered.
Pour 1 tbsp oil into a frying pan and bring to a medium-high heat. When the pan is smoking hot, add the lamb steaks and cook for 5-6 mins on each side, then transfer to a warm plate and allow to rest for 1-2 mins.
While the lamb rests, finish the couscous. Finely chop the parsley. Finely grate the lemon zest. Fluff the couscous with a fork. Stir in the parsley and lemon zest, and squeeze in the juice. Pour in 1 tbsp oil, add a pinch of salt and pepper and stir to combine.
Pile the herby couscous onto plates and top with the roast veg. Slice the spiced lamb steaks, arrange on top of the veg and serve.