Pat the chicken dry, then season with salt and pepper. Heat a thin coating of neutral oil in a large skillet. Add the chicken and cook, undisturbed, until browned. Turn and add the tomatoes, fish sauce and chili; scrape the skillet. Cover and cook until tender, about 20 minutes. Stir in the peanut butter and simmer until thickened. Season with salt and pepper. Sprinkle with lemon zest and juice.