Carefully peel rind off lemons, making sure no pith is included. Cut lemon rind into julienne strips and blanch in boiling water for 3 minutes. Drain, refresh in cold running water and set aside.
Pick leaves from watercress. Wash leaves well the blanch in boiling water for 4 minutes. Drain well and puree in a blender or food processor. Measure 2/3 cup (165 ml) of puree and dilute with sufficient cream so that it will lightly coat an oyster. Keep warm.
Place remaining ingredients in a pan and simmer for 5 minutes.
Remove vegetables and bouquet garnish. Add oyster to pan and poach over gentle heat for 2 minutes. Drain and put oysters back in shells.
Divide oysters recipes between 4 serving plates and coat with watercress sauce. Garnish with lemon strips.