Wash the chicken and bring it to the boil with just under 2 l of cold water in a large pot over medium heat. Skim off the resulting foam with a skimmer.
Soup greens clean or peel, wash and roughly dice. Peel and chop 2 onions. Add soup greens, onions, peppercorns, bay leaf and 1 tsp salt to the chicken. Bring to the boil again and simmer at low heat for about 30 minutes.
Wash the lemon hot, dry and grate the peel thinly. Squeeze the lemon. Peel the remaining onions and cut into strips. Peel garlic and chop finely. Wash chives, shake dry and cut into small rolls.
Remove the meat from the broth. Pour broth through a fine sieve and collect. Heat oil in a pot. Sauté onion strips and garlic in it. Add couscous, steam briefly and deglaze with 1 1⁄2 l chicken stock.
Bring to the boil, then switch off the stove and let the couscous swell covered for about 5 minutes.
In the meantime, remove the flesh from skin and bones. Pluck into small pieces with two forks. Cut the cheese into thin slices. Stir the meat, cheese, lemon peel and chives into the soup. Heat again and season to taste with salt, pepper and lemon juice.