Season both sides of the chicken thighs with 3/4 teaspoon kosher salt and 1/2 teaspoon black pepper. Zest and juice the lemon, finely dice the onion, and mince the garlic. Measure out orzo and have hot chicken broth ready.

Heat the skillet over medium-high heat until hot, then add olive oil. Place chicken thighs skinless-side down and sear, undisturbed, until well browned, about 5–6 minutes. Flip and cook the other side 3 minutes just to brown — you are not cooking through. Transfer chicken to a plate and set aside.

Reduce heat to medium and add butter to the same skillet. Add the diced onion and a pinch of salt; cook, stirring, until softened and translucent, about 3–4 minutes. Add the garlic and lemon zest and cook until fragrant, about 30 seconds.

Add the dry orzo to the skillet and stir to coat in the butter and oil; cook, stirring frequently, until the orzo is lightly toasted and opaque, about 1–2 minutes.

Carefully pour the hot chicken broth into the skillet (it may sputter). Add the lemon juice and the remaining 1/4 teaspoon salt and 1/2 teaspoon pepper. Stir once, bring to a gentle simmer, then nestle the seared chicken thighs into the orzo, spacing them evenly.

Reduce heat to low, cover the skillet, and simmer gently until the orzo is tender and chicken reaches 165°F on an instant-read thermometer, about 12–14 minutes. If orzo absorbs too much liquid before tender, add up to 1/4 cup hot broth or water and continue cooking briefly.

Remove from heat. Stir the Parmesan and chopped parsley into the orzo (tucking the chicken aside while you stir). Taste and adjust salt and pepper. Let the pan rest, uncovered, 3–5 minutes so sauce thickens slightly. Spoon orzo onto plates and top with a chicken thigh each, finishing with extra Parmesan and a squeeze of lemon if desired.