Salmon on Greens with Wasabi Peas

Name: Salmon on Greens with Wasabi Peas
Ingredients: 1 teaspoon sugar; ½ teaspoon finely grated peeled ginger; 2 tablespoons unseasoned rice vinegar, divided; 2 Persian cucumbers, thinly sliced; Kosher salt; 2 scallions; 3 tablespoons white or dark soy sauce; 1 tablespoon plus 1½ teaspoons mirin; 1 tablespoon plus 1½ teaspoons fresh grapefruit juice; 1 teaspoon fresh lemon juice; 5 heads of Little Gem lettuce, cores removed, leaves separated; 12 ounces fresh salmon, cut into ½-inch pieces; 1 avocado, cut into ½-inch pieces; ¼ cup prepared wasabi green peas, crushed; Furikake (for serving)