Season chicken thighs with salt and pepper.
Heat olive oil and 2 tablespoons butter in a large skillet over medium heat.
Cook chicken thighs until golden brown on both sides and cooked through, about 6 to 8 minutes per side. Remove and set aside.
Add remaining butter to the pan. Sauté onion and garlic until softened.
Stir in the orzo and cook for 2 minutes to toast lightly.
Pour in chicken broth, bring to a simmer, and cook until orzo is tender, about 10 minutes.
Return chicken to the skillet, nestling it into the orzo.
Stir in Parmesan cheese, lemon juice, and parsley.
Taste and adjust seasoning, then serve warm.