A bright citrus salsa makes this dish irresistible.
Fill large nonreactive pot with cold water. Quarter two lemons; squeeze juice into water, and add quarters to pot. Trim one artichoke at a time, cutting stem to one-half inch. Remove leaves down to fuzzy choke, and neatly trim bottom of green exterior. Transfer artichoke to water. Repeat for all artichokes. Add 1 1/2 teaspoons salt, peppercorns, bay leaves, garlic, and 1 tablespoon oil. Cover, bring to a boil, and reduce to simmer. Cook, covered, over low heat until tender when pierced in center, 20 to 30 minutes. Drain.
Meanwhile, cook shrimp in boiling water until opaque, 2 to 3 minutes. Strain; place under cool running water to stop cooking. Cut into three-quarter-inch pieces. Set aside.
When artichokes are cool, 15 to 20 minutes, scoop choke; discard. Neatly trim artichoke bottoms; transfer to shallow container. Drizzle with 2 tablespoons oil, 2 tablespoons juice from remaining lemon, 1/4 teaspoon salt, and pepper. Coat artichokes in mixture. May be refrigerated up to one day ahead.
Place the artichokes on a serving dish or platter. Arrange a small lettuce leaf on top of each artichoke. Fill each with shrimp and salsa.
Make the artichoke-bottom recipe first, then proceed with the salsa.