Four 7-ounce whole trout or snapper, gutted and scaled (you can always get your fishmonger to do the dirty work for you)
2 scallions, white part only, thinly sliced
Sea salt and black pepper
Preheat the oven to 375°F. Set a baking sheet inside.
In a bowl, combine the yogurt, mint, chives, lemon zest, lemon juice, and ginger. Mix until well combined.
To create the bag, tear off four 8-by-12-inch sheets of parchment paper. Fold each sheet in half lengthwise, with the two long sides together, then twist the short ends tightly so that they don’t unravel, to close the sides.
Place one fish in each bag and carefully spoon the yogurt mixture over each. Sprinkle with the scallions and some salt and pepper. Close the bag by curling the open side and finish by twisting the two corners.
Carefully remove the hot baking sheet from the oven and place the bags on it. They should sizzle from the heat. Bake for 8 to 10 minutes.
Serve the bags unopened, directly from the oven, on a plate with steamed rice or a fresh salad. The bags should be opened at the table—just be careful of the steam.