Preheat a grill to medium and brush the grates with vegetable oil. Combine 1/2 cup olive oil, the parsley, cilantro, scallions, vinegar and garlic in a blender and pulse until combined. Add the red pepper flakes and season with salt. Pour half of the herb oil into a bowl; set aside for serving.
Toss the swordfish with the remaining 1 tablespoon olive oil, the cumin and coriander in a bowl; season with salt. Thread the swordfish, mushrooms and red onion onto eight 10-inch skewers. Grill the kebabs until just marked, about 2 minutes per side, then continue cooking, turning and brushing with the remaining herb oil, until just cooked through, 5 to 6 more minutes. Drizzle with the reserved herb oil.