Bring a large pot of salted water to a rolling boil. Add the soba noodles and cook according to package directions until just tender (usually 4–6 minutes). Stir occasionally to prevent sticking.
While the noodles cook, whisk together tahini, sesame oil, soy sauce, rice vinegar, honey, lime juice, lime zest, grated ginger, minced garlic and Sriracha in a medium bowl. Add warm water a little at a time until the dressing reaches a smooth, pourable consistency. Set the dressing aside for at least 8–10 minutes to allow flavors to meld.
Drain the noodles and immediately rinse under cold running water to stop cooking and remove excess starch. Shake well, then toss the drained noodles with the neutral oil to keep them separate and glossy.
If using frozen edamame, rinse or briefly blanch and drain. Place carrots, cucumber, edamame and sliced scallions in a large mixing bowl and toss to combine.
Add the cooled, oiled soba to the bowl with the vegetables. Pour about three-quarters of the dressing over the noodles and vegetables and gently toss until everything is evenly coated. Taste and add remaining dressing if you prefer a saucier bowl.
In a dry skillet over medium heat, toast the sesame seeds, stirring frequently, until fragrant and lightly golden, about 2–3 minutes. Remove from heat and let cool briefly.
Divide the dressed soba and vegetables among four bowls. Sprinkle each serving with toasted sesame seeds and chopped cilantro, and finish with an extra drizzle of sesame oil or a lime wedge if desired.
Leftover sauce keeps well refrigerated for up to 4 days — whisk before using. For best texture, store dressing separately from noodles if making ahead.