In a food processor, combine onion, garlic, spice blend, cilantro, green mango pickles, oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Blend until smooth; set marinade aside.
Use a sharp knife to cut 3 slits, about 1/2 inch deep, through the skin of each fish fillet.
Place fillets in a shallow dish and coat them completely with marinade. Cover and refrigerate for 30 minutes.
Preheat a nonstick grill pan over medium-high. Grill fish, skin-side down, until lightly charred, 3 to 4 minutes. Turn fish and continue grilling until fish is cooked through, about 3 minutes more. Serve with okra kebabs and garnish with lemon wedges and cilantro sprigs.