- Put 3 quarts of water in a large stainless steel pot. Add half the boiling spice, 1 bay leaf, 3 garlic cloves, celery, and a small handful of salt. Bring to a boil over medium-high heat, reduce the heat to a simmer, and cook 10 minutes. Raise the heat, add the shrimp, cover, and cook 2 minutes. Drain, rinse under cold running water, peel, and, if you like, devein the shrimp.
- Bring the vinegar, onions, and remaining bay leaf, spice, and garlic to a full boil in a saucepan over medium-high heat, reduce the heat to low, and simmer 5 minutes. Turn off the heat. Let it cool slightly and pour it over the shrimp. Mix in the lemon zest and juice the lemon into it through a strainer. Toss well and let cool completely. Cover and marinate, refrigerated, for at least 4 hours and as long as 24 hours. They will actually keep for up to 2 weeks refrigerated.
- To serve, lift the shrimp from the marinade. If you like, you may dress them lightly with a few spoonfuls of olive oil to taste. Line a platter or shallow serving bowl with lettuce leaves. Mound the shrimp on top of them and garnish with sliced lemon and parsley.