If using live lobsters, steam or boil them. Let cool at room temperature. Use a cleaver to crack and remove the meat from the claws, knuckles and tails. Remove the cartilage from the claws and the intestines from the tails of the cooked meat. Cut the meat into 1/2-inch dice. You may pick all the meat from the carcass and add it to the meat or freeze the carcass for soup or broth.
Place the cucumber in a colander for at least 5 minutes to drain the excess liquid. Combine the lobster, cucumber mayonnaise, and tarragon. Add the scallions. Season with salt and pepper. Cover with plastic wrap and chill for 30 minutes to 1 hour. Preheat a large heavy skillet (12 to 14-inches) over medium-low heat (a black cast-iron pan is perfect). Lightly butter both sides of each bun. Place them in the pan and cook for about 2 minutes until golden brown. Turn the buns over and toast the other side. Or toast the buns under a broiler instead. When the buns are ready, stuff them with the chilled lobster salad. Place each roll on a small paper or china plate; garnish with pickles and potato chips. Serve at once.