Heat olive oil in a large pot over medium heat. Add diced chicken breasts and cook until golden brown on all sides, about 6-8 minutes. Remove chicken and set aside.

In the same pot, add minced garlic, carrots, and celery; sauté until softened (about 3-4 minutes).

Pour in the chicken broth along with thyme sprigs; bring to a boil.

Add the orzo pasta and return to a simmer for about 10 minutes until al dente.

Squeeze in lemon juice and add spinach or kale; stir until greens are wilted.

Adjust seasoning with salt and pepper before serving hot.