Preheat a grill to medium high. Combine the yogurt, cilantro, serrano, ginger, lime juice, 1/2 teaspoon salt and a few grinds of pepper in a blender and puree until smooth. Toss half the sauce with the chicken thighs and curry powder in a medium bowl until coated. Set aside the remaining sauce for serving.
Thread the chicken onto 4 metal skewers, leaving a little space between each piece. Thread the okra onto 4 more skewers. Brush the kebabs all over with the melted butter and season with salt and pepper.
Grill the okra and chicken, turning occasionally, until lightly charred and cooked through, 6 to 8 minutes for the okra and 12 to 15 minutes for the chicken. Grill the naan until lightly charred, about 1 minute per side.
Divide the naan, chicken and okra among plates. Add the tomatoes to the plates and season with salt. Serve with the reserved yogurt sauce.