Thaw scallops or shrimp, if frozen. Rinse scallops or shrimp; pat dry with paper towels. Set aside.
Cook soba according to package directions; drain. Rinse with cold water; drain again. In a medium bowl, toss together spaghetti, cabbage, carrot, and red onion. Transfer soba mixture to a serving bowl; set aside.
Meanwhile, for dressing:
In a small bowl, whisk together vinegar, the 1 tablespoon oil, the soy sauce, honey, and crushed red pepper. Set aside.
In a medium skillet, heat the 2 teaspoons oil over medium heat. Add scallops or shrimp; cook for 3 to 4 minutes or until opaque, turning once to brown evenly. Place scallops or shrimp on top of cabbage mixture. Drizzle dressing over; sprinkle with sesame seeds. Gently toss to coat.