Heat the olive oil or butter in a large heavy-bottomed pot over medium heat until shimmering and fragrant.
Add the minced garlic and cook for about 30 seconds until fragrant, stirring gently.
Toss in the diced chicken and cook for 5-7 minutes, stirring occasionally, until the chicken turns opaque and just starts to brown.
Pour in the chicken broth and bring the mixture to a gentle simmer, around 70°C (160°F), reducing the heat if necessary.
Add the sliced carrots and celery, stirring to combine, then cover and let simmer for about 10 minutes or until the vegetables are tender and flavors meld.
Stir in the chopped greens and cook for another 2-3 minutes until wilted and vibrant, making the soup look lively and colorful.
Finish by squeezing fresh lemon juice into the soup, zesting a bit of lemon peel over the top, and seasoning with salt and pepper to taste.
Garnish with chopped fresh herbs for a bright, fresh aroma before serving hot.
Serve the soup in bowls, enjoying the tender chicken, softened vegetables, and flavorful broth with a slice of crusty bread if desired.