Combine cornstarch and 1 teaspoon water; set aside.
Pat scallops dry with paper towels. Sprinkle scallops evenly with 1/8 teaspoon salt and 1/8 teaspoon pepper.
Heat peanut oil in a large nonstick skillet over medium-high heat. Add scallops to pan; cook 2 minutes on each side or until done. Transfer scallops to a platter. Add garlic to pan; sauté 30 seconds. Add remaining 1/8 teaspoon salt, remaining 1/8 teaspoon pepper, mirin, and next 6 ingredients (through sesame oil). Stir in cornstarch mixture; bring to a boil. Cook 1 minute or until sauce thickens, stirring constantly. Pour sauce over scallops; sprinkle with sesame seeds.