
Place the olive oil in a large sauce pot over medium-low heat. Peel the onion, quarter it, and slice into thin strips. Sauté the onion and minced garlic for 3-4 minutes.
Add chicken broth, chicken breasts, lemon zest, and crushed red pepper. Bring to a boil, then reduce heat and simmer for 5 minutes.
Stir in couscous, salt, and pepper. Simmer another 5 minutes.
Remove chicken breasts, shred, and return to soup. Stir in feta and chives, season to taste.
Serve warm.