Step 1: Make the Sriracha Sauce: In a small food processor or blender, combine the sour cream, mayonnaise, garlic, cilantro leaves, lime juice, and sriracha. Blend until fairly smooth. Transfer to a bowl and refrigerate until serving time.
Step 2: Make the marinade: Place the chile paste, soy sauce, sesame oil, scallions, garlic, sugar, chile powder, and pepper in a nonreactive mixing bowl and whisk to mix. Place the fish in a large resealable plastic bag and pour the marinade over the fish. Turn to coat completely. Refrigerate for 30 minutes.
Step 3: Set up the grill for direct grilling and preheat it to medium-high. Oil the grill basket or wire grid well with vegetable oil. Drain any excess marinade from the fish and discard the marinade. Arrange the fish fillets in a single layer in the basket and lock, or arrange the fish on the grill grid. Place the basket or grill grid on the hot grate. Grill the fish until the fish is white and translucent and breaks into firm flakes when pressed with a finger, 3 to 4 minutes per side.
Step 4: Arrange the fish on a platter and serve with the tortillas, kimchi, lime wedges, and Sriracha Sauce.
Use an expandable grill basket to grill the fish.