Gently remove lump crab from shells. Taste to see if the crab meat is salty or not.
Combine lump crab, salt, black pepper, lemon zest, lemon juice, shallot, capers, chives, and mayonnaise in a bowl.
Gently fold all of the ingredients together, ensuring lump crab meat stays intact.
Place the bowl in the fridge until just before serving.
Cut two thick slices of brioche bread and then cut a pocket down the middle of each.
On medium to medium low heat, melt a tablespoon of butter in a pan and toast both slices of bread until golden brown. Rotate the slices around the pan to ensure both slices brown evenly.
Pick up both slices and repeat step 6 on the other side of the bread. Set bread aside.
When ready to serve, take your crab mixture out of the fridge. Taste and adjust seasoning if needed.
Spread a thin layer of mayonnaise into each slice of brioche, place a leaf of lettuce on top, and generously spoon crab mixture into each sandwich.
Finish with a squeeze of lemon or hot sauce on the crab if you wish. Serve and enjoy.