How to Make It
Cut cucumber in half lengthwise; cut into 1/8-inch-thick half-moons. Set aside.
Prepare soba noodles according to package directions. Drain well, and toss with 1/4 cup sesame oil and salt; set aside.
Whisk together soy sauce, agave, rice vinegar, lime zest and juice, and remaining 2 tablespoons sesame oil in a small bowl until combined. Set aside.
Process white sesame seeds and tahini in a food processor until smooth, about 45 seconds. With food processor running, slowly drizzle in soy sauce mixture, processing until dressing is well combined, about 30 seconds.
Toss together noodles, soy sauce mixture, cucumber slices, and scallions in a large bowl until combined. Divide mixture evenly among 6 bowls. Garnish with sliced scallions and white and black sesame seeds.