Make the dressing: Using a mortar and pestle, crush the garlic, sugar, and Thai chili, if using, into a paste (alternatively, finely mince the garlic and chili into a fine paste, then add the sugar). Transfer to a small bowl and stir in the lime juice, fish sauce, and½ cup of water. Set aside.

Cook the vermicelli according to the package directions. Drain, rinse in cold running water, then drain well.

Bring a medium pot of water to a boil over high heat. Prepare a bowl of ice water. Boil the shrimp until plump, pink, and firm, 2 to 3 minutes, then use a slotted spoon to immediately transfer them to the ice water bath. Once cool, drain well.

Place the noodles in a large serving bowl and add the shrimp, celery, cherry tomatoes, cilantro, and green onions. Drizzle with the dressing to taste and toss to combine, then serve immediately.

Note: Celery leaves are deliciously delicate and complex. If your celery comes with the leaves attached, you should totally add them to the salad in Step 4.