In a medium nonstick skillet, toast 1 nori sheet at a time over medium-high heat, about 5 seconds per side. Tear the nori into large pieces and place in a food processor.
In the same skillet, bring the sugar, oyster sauce, soy sauce and 2 teaspoons water to a simmer over medium heat and cook, stirring, until slightly reduced and syrupy. Add the mixture to the nori in the food processor, along with the egg and 1 tablespoon oil; pulse to combine. Transfer to a medium bowl.
In a medium saucepan, heat the remaining 2 cups oil until it registers 365 degrees on a deep-fry thermometer. Meanwhile, whisk the flour, then the seltzer, into the nori mixture.
Working in batches, dip the pollack in the nori batter, add to the hot oil and fry until golden, about 2 minutes, letting the oil temperature return to 365 degrees between batches. Serve the fish on a bed of cucumber ribbons.