Preheat oven to 375 degrees F. In a 1-cup glass measure, combine 3 tablespoons oil, the vinegar, onions, dill, and tangerine peel; set aside.
Cut fish into 4 equal pieces. Pull out any bones with pliers or tweezers.
Cut parchment into 4 pieces, each about 3 times wider and 3 times longer than seafood portion. In the center of each piece of paper, cover an area the same size as a serving of seafood with about 1/2 teaspoon of melted butter.
For each serving, place 1 piece fish on buttered section of parchment, drizzle with a quarter of the oil mixture, and season to taste with salt and pepper.
To seal packets: Fold long edges of parchment together once over seafood. Crease paper to make a 1/2-inch fold, then fold again two times to seal. With cut end of parchment down, double-fold each end of packet, pressing lightly to crease and tucking ends under. (At this point, you may cover and refrigerate packets up to 1 day.)
Place packets slightly apart, folded ends down, on a large baking sheet; brush lightly with oil. Bake until packets are puffed up and golden, about 7 to 9 minutes.
Transfer to dinner plates. To serve, cut open packets with a sharp knife or scissors just enough to expose contents without letting juices run out. A blast of aromatic steam when you open your packet lets you know how juicy the fish inside will be.