Another firm-fleshed fish, such as halibut or salmon, can be substituted for the striped bass. Broilers vary in heat intensity; move the rack to a lower position if the cauliflower or fish is browning too quickly, or to a higher rack if too slowly.
Preheat broiler with rack 6 inches from heating element. Place cauliflower on a rimmed baking sheet and brush with 2 tablespoons oil; season with salt and pepper. Spread in a single layer and broil until crisp-tender and golden brown in spots, 10 minutes.
Drizzle fish with remaining 1 tablespoon oil; season generously with salt and pepper. Place on top of cauliflower, skin side up, and add capers to sheet. Broil until fish is just opaque throughout, 5 to 7 minutes. Add raisins and broil just until plump and hot, about 30 seconds. Drizzle fish and vegetables with vinegar, and divide evenly among 4 plates. Serve sprinkled generously with herbs and drizzled with more oil.