Heat olive oil in a large pot over medium heat. Add onion, carrots, and celery. Sauté for 5-7 minutes until vegetables begin to soften.

Add minced garlic and cook for another minute until fragrant.

Pour in the chicken broth and bring to a gentle boil. Add the orzo and cook for about 7-8 minutes, or until it's almost al dente.

While the orzo cooks, prepare the egg-lemon mixture (avgolemono): In a medium bowl, whisk eggs until light and frothy. Slowly whisk in the lemon juice.

Here's the crucial part: Temper the egg mixture by slowly adding about 1 cup of hot broth while continuously whisking. This prevents the eggs from scrambling.

Reduce heat to low and slowly pour the tempered egg-lemon mixture into the soup, stirring constantly.

Add the shredded chicken and spinach (if using). Cook for 2-3 minutes until the chicken is heated through and the spinach wilts.

Stir in fresh dill and season with salt and pepper to taste.