In a large pot, heat the olive oil over medium heat. Once hot, add the finely chopped onion, diced carrots, and diced celery. Sauté for about 5-7 minutes, stirring occasionally, until the vegetables are softened and the onion is translucent.
Add the minced garlic and dried oregano to the pot. Stir the mixture and sauté for an additional minute, allowing the garlic to become fragrant without burning.
Pour in the vegetable broth and increase the heat to bring the mixture to a rolling boil. Once boiling, add the dry orzo pasta. Cook according to the package instructions, typically around 8-10 minutes, stirring occasionally to prevent sticking.
Once the orzo is tender, lower the heat. If using, stir in the shredded cooked chicken. Then add the chopped baby spinach, freshly squeezed lemon juice, and lemon zest. Mix everything thoroughly and cook for an additional 2-3 minutes, or until the spinach is just wilted.
Taste the soup and season generously with sea salt and freshly ground black pepper according to your preference. Remove the pot from the heat and let the soup rest for a few minutes to thicken slightly.
Serve the soup hot, garnished with fresh dill sprigs if desired.
Notes
Optional to add cooked chicken for extra protein. Garnish with fresh dill for added flavor.