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.
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.