Combine the lemon juice, olive oil, vinegar, seafood seasoning, dill, parsley, mustard, chile, garlic, lemon slices and onion in a large bowl, toss together and set aside.
In a large pot of boiling water, add the kosher salt. Add the shrimp and cook just until they begin to turn pink and float to the top, about 2 minutes. Drain and immediately add them to the pickling liquid.
Let stand for 5 to 10 minutes at room temperature and then serve. Or refrigerate until you are ready to serve them.
Serve with Lemon Chive Aioli for dipping.
Lemon Chive Aioli:
Combine the mayonnaise, lemon juice, chives, lemon zest and garlic in a small mixing bowl and whisk until fully combined. Serve alongside the pickled shrimp.;