Put the potatoes in a 6- to 8-quart slow cooker. Toss the chicken with the ginger, curry powder, cumin, 1/2 teaspoon salt and a few grinds of pepper. Lay on top of the potatoes and sprinkle with the serrano. Whisk the tomato sauce and tomato paste together and pour over the chicken. Cover and cook on low until the potatoes and chicken are very tender, 7 to 8 hours.
Uncover the slow cooker and gently remove the chicken. Add the okra and cilantro to the slow cooker, cover and cook until tender, about 10 minutes. Meanwhile, discard the bones and cartilage from the chicken but leave the meat in large pieces. Return the chicken to the slow cooker and gently stir a few times to coat in the sauce. Season with salt and pepper.
Divide the curry among shallow bowls. Top with more cilantro and serve with the naan.