In a large, deep skillet with a tight fitting lid, heat the oil over medium heat. Once its hot, add the onion. Cook, stirring often until it's translucent, about 5-7 minutes. Then stir in the garlic and cook another minute or so more, until it's fragrant. Increase the heat to med-high and add the orzo to the pan and let that toast a bit, stirring often.

Stir in the broth, diced tomatoes, chicken and seasonings. Let it come up to a low boil. Once starting to boil, cover with a lid and reduce the heat to med-low. Let this simmer covered for 12-15 minutes, or until the liquid has absorbed, stirring often. In the last few minutes of cook time, stir in the chopped spinach. Then serve with some fresh parmesan on top.