Season chicken on both sides with salt and pepper.
Heat olive oil or butter in a deep pan over medium heat.
Sear chicken until golden, about 3 minutes per side. Remove and set aside.
In the same pan, add onion and cook until soft.
Stir in garlic and sun-dried tomatoes. Cook for 30 seconds.
Pour in chicken stock and milk or cream. Stir well.
Add orzo and scrape the pan bottom to release flavor.
Place chicken back into the pan.
Reduce heat and simmer for 15–18 minutes, stirring often.
When orzo is tender, lower heat and stir in cheese.
Add spinach and let it wilt.
Taste and adjust seasoning. Add lemon if desired.
Rest for 1 minute, then serve warm.