Bring a large pot of salted water to boil and cook the orzo until partially cooked, but not fully cooked (about 5 minutes). Drain the pasta, rinse with cold water to stop the cooking, and set aside.
While the orzo is cooking, heat another large pot over medium high heat, add the olive oil, then add the chopped onion. Cook until translucent, 5-7 minutes.
Add the minced garlic to the onion and stir.
Season the mixture with oregano, salt, pepper, and bay leaf. Stir and cook for about 30 seconds.
Pour in the chicken broth.
Bring the broth to a boil and simmer for about 5 minutes.
Stir in the cooked orzo, lemon juice, lemon zest, and chopped cooked chicken. Cook until the chicken is heated through.
Add in the baby spinach and cook until the spinach is wilted, about 2-3 minutes.
Ladle into bowls and serve.