Step 1

Toast pistachios in a dry small skillet over medium-low heat, tossing occasionally, until browned in spots, about 5 minutes. Let cool, then finely chop.

Step 2

Gently mix pistachios, prunes, garlic, parsley, mint, tarragon, kimchi brine, and vinegar in a medium bowl to combine; season with salt. Whisk in oil, then taste and season spoon sauce with more saltif needed.

Step 3

Prepare a grill for medium heat. Using a chef’s knife, cleaver, or serrated knife, cut fish crosswise into 2"–4"-wide planks (the larger the fish, the wider the planks); halve planks if fish is large. Pat fish dry, rub all over with oil, and season with salt and Aleppo-style pepper. Grill fish, undisturbed, until about 70 percent cooked through (use a knife to slide into flesh to check), about 5 minutes. The skin should release easily from the grate when the fish is ready to turn. If it’s sticking, keep cooking.

Step 4

Using a large fish spatula, turn fish over and grill until cooked through (fish is done when a paring knife easily pierces the flesh along the side), about 2 minutes.

Step 5

Transfer fish to a platter and spoon sauce over.