1. Cook soba according to package instructions. Drain in a colander and rinse with cold running water until noodles are cold. Drizzle with 1 tbsp. canola oil, tossing to coat so noodles don't clump together.
2. Meanwhile, heat remaining 1 tbsp. canola oil in a large frying pan over medium-high heat. Add shrimp and cook just until pink and cooked through, about 4 minutes. Remove from heat.
3. Whisk together harissa, soy sauce, vinegar, sesame oil, and a pinch of salt in a small saucepan. Cook over medium heat until just warmed through, about 2 minutes.
4. Transfer drained noodles to pan of shrimp and toss with dressing. Divide among 4 bowls, then top with radishes, green onions, and sesame seeds.
*Find soba noodles and harissa at well-stocked grocery stores.