Combine cabbage and radishes in a large bowl; set aside.
Combine rice vinegar, soy sauce, 1 teaspoon oil, and red pepper, stirring well with a whisk.
Heat remaining 1 teaspoon oil in a large nonstick skillet over medium-high heat. Sprinkle scallops with salt and black pepper. Add scallops to pan; cook 3 minutes on each side or until done. Arrange 1 cup cabbage mixture on each of 4 plates; top each serving with 4 scallops. Drizzle each serving with 1 tablespoon vinegar mixture; sprinkle each serving with 1/2 teaspoon sesame seeds. Serve immediately.