Slice lobster meat from tail and claws into crosswise pieces, about 3/4-inch thick. Spread the mayonnaise on the brioche slices, and place them in a row on your work surface. Arrange half the tomato slices, greens, bacon, and lobster between 2 slices of brioche.
To assemble, stack the second layer on top of the first with ingredients facing up. Place the last piece of brioche, mayonnaise side down, on top of the second layer. Pierce opposite corners of the sandwich's top layer with lobster picks or decorative toothpicks. Slice the sandwich on the diagonal with a serrated knife.
In a food processor with a metal blade, blend the zest, half the lemon juice, and egg yolks. Slowly add oil in a thin stream until mixture emulsifies and thickens. Season with remaining lemon juice, then salt and pepper, to taste.
Yield: about 1 1/4 cups
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