In a small bowl, mix olive oil, minced garlic, lemon juice, lemon zest, oregano, salt, and black pepper. Rub the mixture all over the chicken thighs and let them marinate for at least 10 minutes.
Heat a large skillet over medium-high heat. Once hot, add the marinated chicken thighs skin-side down and sear for about 5-7 minutes until golden brown and crispy. Flip the chicken and sear for another 5 minutes on the other side.
Remove the chicken thighs from the skillet and set them aside on a plate. In the same skillet, add the orzo and stir for about 1 minute.
Pour in the chicken broth and bring it to a simmer. Return the chicken thighs to the skillet, nesting them in the orzo.
Cover the skillet with a lid and reduce the heat to low. Cook for about 20-25 minutes until the chicken is fully cooked and the orzo is tender, stirring occasionally.
In the last 5 minutes of cooking, stir in the fresh spinach until wilted.
Once everything is cooked, remove the skillet from heat and let it sit for a few minutes before serving.
Garnish with chopped parsley if desired, and serve hot.