Heat oil in a large heavy pot over medium-high heat. Add onions and sauté until tender and starting to caramelize, about 8 minutes. Stir in garlic and next 4 ingredients and cook until fragrant, about 1 minute. Add broth and lemon zest and bring to a boil. Reduce heat to medium; stir in chicken, artichoke hearts, and carrots; simmer until vegetables are tender and chicken is just cooked through, 10–15 minutes. Season to taste with salt and pepper. Divide couscous among shallow bowls; spoon stew over and garnish with parsley