Preheat the oven to 350°F (175°C) and position the rack in the middle.
Season the chicken thighs on both sides with Kosher salt and black pepper.
Heat a 9–10 inch cast iron or ovenproof skillet over high heat and add 2 tablespoons oil.
When the oil is hot, add the chicken (skin side down if using skin-on) and brown 4–5 minutes per side until golden; transfer chicken to a plate.
Reduce heat to medium, add the minced garlic to the same pan and cook, stirring, for about 1 minute.
Add 1/4 cup water, 2 tablespoons soy sauce, 2 tablespoons lemon juice, 1/3 cup honey, and 1 tablespoon minced ginger (if using) to the pan; simmer over medium until the sauce reduces and thickens slightly, about 5–8 minutes.
If you prefer a thicker sauce, mix 2 tablespoons cornstarch with 3 tablespoons water until smooth and stir the slurry into the sauce; cook until thickened, then transfer the sauce to a bowl and set aside.
Lower heat to medium-low and add 1 tablespoon unsalted butter to the skillet; when melted, add the diced onion and cook 1 minute, stirring.
Add the 1 cup dry basmati rice, 1 teaspoon dried rosemary, and 1 tablespoon lemon zest to the skillet; stir and cook 1 minute to toast the rice slightly.
Pour in 2 cups low-sodium chicken broth, season with salt and pepper to taste, and stir to combine.
Return the browned chicken to the pan, placing it on top of the rice (skin side up if applicable).
Cover the skillet tightly with foil and bake in the preheated oven for 45–50 minutes, until the rice is tender and the chicken is cooked through.
Five minutes before the end of baking, remove the foil, brush the chicken with the reserved honey lemon sauce, and broil for 5 minutes to glaze and brown the top.
Let rest briefly, then serve with lemon slices, chopped fresh parsley, and extra sauce on the side.
