Season the chicken thighs on both sides with 1 teaspoon kosher salt, ¼ teaspoon ground black pepper, and 1 teaspoon Italian seasoning.
Heat 2 tablespoons olive oil in a large cast iron skillet over medium-high heat until shimmering.
Add the chicken thighs and brown 3–4 minutes per side until golden; remove chicken to a plate.
Add the remaining 2 tablespoons olive oil to the skillet, then add the chopped onion and a pinch of salt; cook 2–3 minutes until softened.
Stir in the minced garlic and chopped sun-dried tomatoes and cook 1 minute until fragrant.
Add the orzo to the pan and toast, stirring, for about 1–2 minutes.
Pour in 3 cups low-sodium chicken broth and bring the mixture to a boil, then reduce to a simmer.
Return the browned chicken thighs to the skillet, cover, and simmer 10–15 minutes until the orzo is tender and the chicken is cooked through.
Remove the chicken to a plate; stir the fresh spinach, heavy cream, and grated Parmesan into the orzo until the spinach wilts and the sauce is creamy.
Return the chicken to the skillet to warm through, then finish with chopped fresh parsley, additional Parmesan if desired, and a squeeze of lemon juice to taste.
