Heat olive oil in a large pot over medium heat. Add onion, carrots, celery, and garlic; cook and stir until onion is translucent, about 5 minutes. Stir in baby spinach.
Pour chicken broth, diced tomatoes, and lemon juice into the pot. Stir in pepper, oregano, and basil. Bring to a boil, then stir in chicken and rice. Reduce the heat to medium low and simmer until the flavors combine, about 30 minutes.
Chicken Florentine Soup · Dinner Match Lab | Dinner Match Lab