Bring pot of water to boil with 1 tablespoon salt. Add shrimp. Once water returns to slight simmer, strain shrimp and rinse with cold water. Peel shrimp. For a nice presentation leave the tails on.
Course grind mustard seeds and peppercorns with mortar and pestle or spice grinder. In measuring cup or Mason jar combine spices, garlic, capers, lemon zest, juice, vinegar and oil; whisk or shake well to combine.
Place shrimp, thinly sliced onion, hearts of palm, artichoke hearts and peppers in non-reactive bowl and toss with vinaigrette. Cover and refrigerate for at least 6 hours or overnight, occasionally stirring contents to evenly coat.
Serve with baguette or toast points to help sop up all that delicious pickling liquid.