Step 1

Whisk sugar, ginger, and 1 Tbsp. vinegar in a small bowl. Toss cucumbers and a pinch of salt in a sieve, then gently massage cucumbers to expel excess liquid. Add cucumbers to sugar mixture; cover and chill until cold, at least 30 minutes. Taste pickled cucumbers and season with more salt if needed.

Step 2

Meanwhile, remove dark green tops from scallions and thinly slice on a diagonal; transfer to a small bowl of ice water and let sit until scallions begin to curl, 10–15 minutes. Drain scallion tops, then squeeze out excess liquid with paper towels.

Step 3

Thinly slice pale green and white parts of scallions, then whisk in a medium bowl with soy sauce, mirin, grapefruit juice, lemon juice, and remaining 1 Tbsp. vinegar to combine. Transfer 3 Tbsp. ponzu to a second medium bowl. Add lettuce to bowl used to make ponzu; toss to coat and season with salt. Add salmon to second bowl with 3 Tbsp. ponzu and gently toss to coat. Add avocado, drained pickled cucumbers, and scallion tops to bowl with salmon and toss again. Season with more salt if needed.

Step 4

Divide dressed lettuce among bowls. Top with salmon mixture and wasabi green peas; sprinkle with furikake.

Step 5

Do Ahead: Cucumbers can be pickled 3 days ahead; keep chilled. Ponzu can be made 1 day ahead; cover and chill.