Cut the stems off of the artichokes at the base of the globe. To trim the artichokes, use a serrated knife to cut off the top 1/3 of the artichoke leaves. Then, using kitchen scissors, cut off the sharp part of the leaves, about the top quarter of the leaf. Rub lemon juice on the cut part of the artichokes so they don't discolor.
Fill a large stock pot with water and add the artichokes, mustard seed, peppercorns and kosher salt. Boil for about 35-45 minutes or until bottom stem can be pierced easily with a fork and the leaves pull easily from the artichoke. Depending on the size of your artichokes the cooking time will vary.
While the artichokes are cooking, prepare the shrimp salad. Rinse the salad shrimps and pick through for any shells. Place in a medium size bowl and add the green onions and cilantro. Stir to combine. In a small bowl, combine the seasoned rice vinegar, vegetable oil, fish sauce, lime juice, sugar and crushed red pepper flakes and stir until sugar is dissolved. Pour over the shrimp, stir and refrigerate until the artichokes are done cooking.
Once the artichokes are tender, use tongs to pull from the hot water and place upside down on a platter to drain. The leaves will have some of the mustard and peppercorn seeds stuck in between them, and that's okay.
Using a hand held strainer, reserve the cooked mustard seeds and peppercorns from the cooking water. Discard the peppercorns but add the mustard seeds to the shrimp salad.
Once the artichokes are cool enough to handle, open the middle of the choke and pull out the middle leaves that surround the heart of the artichoke. This will leave some fuzzy parts. Use a spoon to gently dig those out of the heart. Discard the fuzzy parts and the middle leaves.
Serve at room temperature with the shrimp salad spooned into the center of the artichoke. Eat the shrimp with the tender leaves as spoons and dunk the leaves into the extra Thai salad dressing if desired.