Heat your oven to 200°C/Fan 180°C/Gas 6.
Peel and grate or crush the garlic. Zest and juice the lemon. Whisk half of the zest and juice with all the garlic and 1 tbsp oil in a bowl. Finely chop the rosemary leaves and add those too. Season with salt and pepper.
Place the chicken breasts in a roasting tin. Pour over the garlicky rosemary marinade and turn the chicken over a couple of times to coat. Pour in 100ml cold water. Put in the oven and roast for 25 mins.
Meanwhile, tip the couscous into a bowl and season with a pinch of salt and pepper. Pour in 250 ml boiling water. Cover with cling film or a plate. Set aside to soak.
Trim the courgette. Using a peeler, peel ribbons from the courgettes, turning as you go so you get long strips off all the sides. Discard the seeded middles. Pop the courgette ribbons in a bowl.
Whisk the remaining lemon zest and juice with 1 tbsp oil. Season. Pour it over the courgettes to wilt them slightly. Fold through the couscous. Taste and season.
Insert a sharp knife into the chicken to check if it’s cooked. The flesh should be white and the juices should run clear. If not, cook for a few mins more.
Serve the rosemary chicken with the courgette ribbon couscous, spooning over the rosemary juices from the roasting tin.