Place a dry frying pan on a medium heat. Add 1 tsp coriander seeds and toast for 2-3 mins, shaking the pan occasionally, till they smell aromatic and start to pop. Tip into a mortar and pestle and roughly crush them, or use a small bowl and a jam jar or rolling pin. Set aside.
Peel and finely chop the onion. Dice the tomatoes. Peel and grate or crush the garlic clove.
Put the frying pan back on a medium heat and warm it for 2 mins. Add 1 tbsp oil and the mince. Fry for 5 mins, stirring and using a wooden spoon to break up any lumps.
When the mince has browned, add the onion and tomatoes to the pan. Pop on a lid (or use a baking tray to cover the pan if you don't have a lid) and cook, stirring once or twice, for 10 mins, till the onion has started to soften.
Stir the garlic into the pan with the ground coriander and 1 tsp each ground cumin and sumach. Season with a good pinch of salt and pepper. Cook and stir for 2 mins till aromatic.
Pour 150ml boiling water into the pan. Pop the lid back on and simmer for 10 mins till the sauce thickens and the mince is tender.
While the mince simmers, tip the couscous into a heatproof bowl. Pour in 300ml boiling water and a pinch of salt. Stir, then cover the bowl with a plate and leave to soak. The couscous will suck up the water. Finely chop the mint leaves.
Stir the spinach into the mince to just wilt it. Taste the mince and add a pinch more salt or pepper if you think it needs it.
Fluff the couscous with a fork and scoop it into 2 warm bowls. Spoon over the spiced mince. Top with spoonfuls of the yogurt, scatter with the chopped mint and sprinkle with a little more sumach to serve.