1. Preheat oven to 400 degrees F. Cut the salmon into four equal pieces and place them on a foil-lined and lightly oiled sheet pan. Sprinkle fish with lemon juice, salt, and pepper. Bake to desired doneness (15-18 minutes).
2. While salmon is cooking, whisk together the sesame oil, soy sauce, rice wine vinegar, and wasabi paste. Add the cucumber, avocado, scallions, and nori and toss to coat. Set aside.
3. Top fish with salsa and sprinkle with sesame seeds.