Heat olive oil in a dutch oven or a 5-quart pan/skillet set over medium-high heat.
Add chicken pieces to the skillet, season with thyme, garlic powder, paprika, salt and pepper, and cook over medium heat until done; about 8 minutes, stirring occasionally.
Remove chicken from the pot and set aside.
Add about 3-quarts of water to the pot; set it over high heat and bring to a boil.
Stir in the orzo and cook for 8 to 9 minutes, or until orzo is tender.
Put the orzo back in the pot and stir in the cheese, milk, butter, and mustard, if using. Continue to stir until smooth, creamy, and well combined. Add more milk if needed to reach desired creamy consistency.
Taste for seasonings and adjust accordingly.
Stir in the spinach; stir for a minute, or until wilted.
Stir in the chicken.