Heat 1 tbsp. oil in a large skillet over medium-high heat until simmering; add chicken and cook until golden brown, about 4-5 minutes per side.
Continue to orzo instructions, keeping chicken in the pan.
Add 1 tbsp. oil to skillet over medium-high heat until simmering; add onion and sauté until softened and fragrant, about 3 minutes.
Add garlic and orzo, season with salt and pepper, and sauté until fragrant, about 1 minute.
Stir in the broth and milk and bring to a boil. cover, reduce to a simmer, and cook, stirring occasionally, until the orzo is al dente and most of the liquid is absorbed and has formed a creamy sauce, about 10 minutes.
Stir in the spinach and parmesan until the spinach has just wilted and the cheese melts, about 1 minute.
Taste and season with salt and pepper as needed.
Garnish with additional cheese if desired.
