Fill a large steamer or pot with about 2 inches of water. Add 1 tablespoon sea salt and bring to a boil over medium heat. Put 2 lobsters (about 1 1/2 pounds each) in the steamer basket or directly in the pot; cover and steam until the shells turn bright red, 8 to 10 minutes. Remove the lobsters and rinse under cold water until slightly cool. Remove the meat from the shells and roughly chop; chill the meat. Mix 1/3 cup mayonnaise, 1/4 cup diced celery, and the zest and juice of 1 lemon in a bowl. Stir in the chilled lobster meat and season with salt. Divide among 4 split-top hot dog buns and top with celery leaves.