Woodland Bundles

Bring water to a boil with 1/2 teaspoon salt. Pour over bulgur in a heatproof bowl and let stand, uncovered, until bulgur is tender but still chewy, about 15 minutes. Drain well in a sieve, then transfer to a bowl. Add trout, currants, pine nuts, lemon juice, walnut oil, and 1/2 teaspoon each of salt and pepper, stirring gently to combine.
While bulgur stands, bring a 6- to 8-quarts pot of salted water to a boil (2 tablespoons salt for 4 quarts water) and add baking soda. Blanch romaine leaves in batches until slightly wilted but still bright green, about 1 minute. Remove with tongs and plunge into an ice bath.
Line a work surface with 3 layers of paper towel, then arrange 2 lettuce leaves, rib sides down, on paper towels. Top with 3 more layers of paper towel, then roll over leaves with a rolling pin, crushing ribs. Remove top layers of paper towel. Trim enough from bottom of each leaf to form an 8-inch-long leaf. Repeat with remaining leaves, replacing paper towels as needed. (You will have 4 extra leaves, in case any tear.)
Arrange 1 leaf with wider end nearest you. Put 2 tablespoons of filling 1 1/2 inches from bottom of leaf. Roll up, gently squeezing to compact filling and keeping a 1/2-inch border on either side free of filling, and fold in sides as you roll. Transfer, seam side down, to a plate. Make 15 more bundles in same manner. Just before serving, drizzle with walnut oil.