Dice the onion, mince the garlic, peel and slice the carrots into 1/4-inch rounds, slice the celery, and finely grate the ginger. Melt the butter with olive oil in a large pot over medium heat. Add the diced onion and cook for 3-4 minutes until it begins to soften and turn translucent. This initial cooking of the onion allows it to release its natural sweetness, which forms the flavor foundation of the soup.
Add the minced garlic and finely grated ginger to the softened onion and cook for about 1 minute, stirring constantly, until fragrant. Then add the sliced carrots, celery, turmeric, salt, and black pepper. Continue cooking for 5-7 minutes, stirring occasionally, until the carrots begin to soften slightly. I like to cook the aromatics this way because it allows the turmeric to bloom in the fat and develop its earthy, warm flavor rather than tasting raw or dusty.
Stir in the shredded rotisserie chicken, breaking up any clumps to distribute it evenly throughout the pot. Pour in the chicken stock and add the parmesan rind, which will gently infuse the broth with savory umami flavor as it simmers. Bring the mixture to a boil over medium-high heat, then reduce to a simmer. The parmesan rind will soften slightly but won't fully dissolve—you'll remove it before serving.
Stir in the couscous and simmer for 10-15 minutes, stirring occasionally, until the couscous is tender and has absorbed much of the broth. The soup should have a thick, hearty consistency with visible broth rather than being completely absorbed. Taste and adjust salt and pepper as needed. I always taste before adding the lemon because the acidity can make it harder to gauge the salt level accurately.
Remove from heat and fish out the parmesan rind with a spoon or tongs. Stir in the lemon zest and fresh lemon juice, then gently fold in the fresh herbs (parsley and dill). Taste again and add more salt, pepper, or lemon juice if desired. The brightness of the lemon and freshness of the herbs should complement rather than overpower the rich, warming broth.
Ladle the soup into bowls and garnish generously with freshly grated parmesan cheese, additional fresh herbs if desired, and a squeeze of fresh lemon. Serve alongside warm crusty bread for dipping and soaking up the flavorful broth.