Prep the shrimp: prepare grill or grill pan for medium-high heat. Whisk fish sauce, sesame oil, and chile flakes in small bowl; add shrimp and toss to coat. Set aside to marinate, 15 minutes.
Prep the salad: whisk together gochujang, vinegar, and sesame oil in medium bowl. Add herbs, carrots, cucumber, and radishes and toss to combine; season with salt.
Grill the shrimp: Lightly brush grill with oil. Season both sides of shrimp with salt and pepper and grill, turning once, until opaque throughout, about 4 minutes.
Serve shrimp on top of salad and sprinkle with sesame seeds.