Preheat the broiler to high if you plan to broil at the end.
Heat a large oven-safe skillet over medium-high heat and add 2 tablespoons butter.
Add the chicken and sliced onion to the skillet and sear until the chicken is browned on the outside and the onions start to soften, about 3–4 minutes.
Add the chopped garlic, ground ginger, chili powder, chipotle chili powder, turmeric, cumin, and season with salt and black pepper; cook and stir until fragrant, about 2–4 minutes.
Pour in 1 cup water, add the cubed sweet potatoes, crushed tomatoes, and coconut milk; stir to combine and bring to a simmer.
Reduce heat to maintain a gentle simmer and cook until the sweet potatoes are tender and the sauce has thickened, 10–15 minutes.
Stir in the remaining 2 tablespoons butter and half of the chopped cilantro.
If desired, place the skillet under the broiler for 3–5 minutes to crisp the top of the chicken—watch closely to avoid burning.
Meanwhile, combine the remaining cilantro with the chopped peanuts and lemon or lime juice; season with salt to taste.
Serve the chicken and sauce over rice with naan on the side, and top each portion with the cilantro-peanut mixture.
