• Soften the dried chiles: Remove the stems and most of the seeds. Cover the chiles with hot water and soak for 15–20 minutes. Drain.
• Blend the sambal: Blend the softened chiles, fresh chiles, shallots, garlic, lemongrass, shrimp paste, and 2–3 tablespoons water into a thick paste.
• Cook the sambal: Heat ¼ cup oil in a skillet over medium-low heat. Add the chili paste and cook for 10–15 minutes, stirring frequently, until darkened, fragrant, and glossy. Mix the tamarind concentrate with 2 tablespoons warm water, then stir it into the sambal with the brown sugar and salt. Cook for another 2–3 minutes. Taste and adjust the salt, sugar, or tamarind. Let cool slightly.
• Season the fish: Pat the stingray dry. Rub it with lime juice, turmeric, and ¾ teaspoon salt. Let stand for 10 minutes.
• Prepare the grill: Heat a grill to medium-high, about 400°F. Place the banana leaf on a large sheet of foil for support and lightly brush it with oil.
• Assemble: Spread a thin layer of sambal over the banana leaf. Place the fish on top and coat generously with more sambal, reserving a little for serving. Loosely fold the leaf and foil around the fish, leaving a small opening for steam to escape.
• Grill: Grill for 6–8 minutes per side, depending on thickness. Open the packet during the final 2–3 minutes for a lightly charred finish. The fish is ready when opaque, easily separates from the cartilage, and reaches 145°F internally.
• Serve: Serve hot with the reserved sambal and lime wedges. Steamed rice, sliced cucumber, and grilled vegetables make good accompaniments.

Broiler option:

• Broiler option: Place the banana-leaf-lined fish on a baking sheet and broil 6–8 inches from the heat for about 10–14 minutes, turning once if practical.