Heat the olive oil in a large pot over medium-high heat. Add in the onion, garlic, carrots, celery, and lemon zest and season with salt and pepper. Cook until the veggies are slightly tender (about 6 minutes) and then add in the chicken, spinach, scallions, lemon juice and chicken stock.
Turn the heat up and let everything come to a boil and then turn off the heat.
Place a scoop of couscous in the bottom of you bowl and then ladle the soup over the top. Finish with a few extra scallions and some lemon zest and enjoy!