- 1 cup sliced shitake or crimini mushrooms, divided
- 1 teaspoon grated fresh ginger, divided
- 4 (4- to 6-ounce) tuna fillets, divided
- Drizzle of toasted sesame oil
- Salt and pepper, to taste
- 2 teaspoons white or yellow miso, divided
- 4 teaspoons mirin, divided
- 4 teaspoons sliced green onions, divided
Preheat oven to 425° F. Cut 4 (18- by 13-inch) pieces of parchment. Fold each piece in half and cut out a large heart shape.
Place 1/4 cup mushrooms and 1/4 teaspoon ginger on one side of a parchment paper heart. Lay 1 fish fillet on top of the vegetables, sprinkle with salt and pepper, and drizzle with a little oil. Top with 1/2 teaspoon miso, 1 teaspoon mirin and 1 teaspoon green onions.
Repeat with remaining ingredients and parchment hearts.
Beginning at the top of each heart, make small overlapping folds, picking up both sides of the paper. Crease the folds well and make sure each new fold overlaps the previous fold. Twist the tail end under to seal.
Transfer packets to a baking sheet. Bake until fish is cooked through, the packets are puffed and starting to color, 12 to 14 minutes.
Transfer packets to serving plates and use scissors to cut a small X in the top of each packet. Tear open carefully (the packets will release steam).