1 Remove peel (including white pith) from 2 oranges, then cut the flesh into slices. Squeeze out juice from remaining orange.
2 Peel the cucumber, cut in half lengthwise, remove the seeds with a spoon and cut the flesh into very thin slices.
3 Rinse the lettuce, spin dry and cut or tear into bite-sized pieces.
4 Rinse the tarragon, shake dry, pluck leaves and coarsely chop. Place in a bowl with the lettuce, cucumber and orange slices.
5 Squeeze out lime juice. In a bowl, mix together 1 tablespoon lime juice and 3 tablespoons orange juice, then season with a little salt and pepper and whisk in the oil.
6 Peel and devein the shrimp, then rinse briefly and pat dry well.
7 Crush the coriander seeds and peppercorns in a mortar or with the side of a large knife. Sprinkle over the shrimp.
8 Cook the shrimp on an oiled hot grill or in a grill pan until seared, about 45 seconds on each side. Season lightly with salt.
9 Toss the salad mix with the citrus dressing, top with shrimp and serve immediately.