Cook the rice vermicelli according to package instructions (I soaked mine for 10 minutes in warm water). Drain and rinse with cold water.
In a medium bowl or jar, combine all the sauce ingredients. Whisk or shake until well combined, set aside.
Bring enough water (with a big pinch of salt) to a gentle simmer in a medium pot. Add the shrimp and poach for 2–3 minutes until they turn pink. Immediately transfer them to an ice bath, drain, and add to the dressing to marinate.
In a large bowl, combine the cooled noodles, sliced cucumbers, red bell pepper, and chopped fresh herbs (excluding the reserved herbs). Add the shrimp and sauce and toss well to combine. Chill for at least 15 minutes before serving.
