In a glass baking dish or a wide, shallow, nonreactive bowl, mix together olive brine and lemon juice. Gently toss in tuna slices and olive slivers. Cover and refrigerate for 2 hours, occasionally moving tuna slices around gently in marinade to ensure that slices cure evenly.
Just before serving, strain the tuna slices from marinade. Divide tuna between 4 to 6 appetizer plates. Spoon a little marinade (with olive slivers) over the tuna. Grind black pepper, to taste, over each serving. Garnish with fennel and lemon zest, and serve immediately.
2008, Michael Symon, All Rights Reserved.