Preheat oven to 450 degrees. Salt fish on both sides. Finely grate zest of 1 lemon over fillets. Sprinkle on 1 tablespoon oregano.

In a bowl, toss tomatoes with vinegar and 3 tablespoons oil. Stir in 2 minced garlic cloves and season with salt. Lightly crush tomato mixture until juices pool in bowl. Toss in snow peas

Arrange each halibut fillet on a rectangle of parchment paper, leaving a 2-inch border all the way around. Place each parchment rectangle on a rectangle of aluminum foil, leaving a 1-inch border of foil all around. Spoon tomato-snow pea mixture and some of juices over fish. Pour 1 tablespoon wine over each fillet.

Top each serving with a second paper rectangle of equal size to the first, and fold edges to make a parcel. Fold foil over edges and crimp to seal. Place parcels on 2 baking sheets and bake until paper puffs and browns and fish is easily pierced with a knife and flakes when prodded,, about 15 minutes.

In a mortar, combine remaining oregano and garlic. Finely grate in zest of 1 lemon. Add juice of 1 lemon and remaining oil. Smash with pestle to form a chunky sauce. Add more lemon juice, oil and salt to taste.

Cut open parcels at table and drizzle oregano sauce over contents. Serve with new potatoes, salad or both.