1/2 lemon, sliced paper thin, plus 1 teaspoon lemon juice
1 bunch watercress (6 ounces), large stems discarded
Light a grill or preheat the broiler. In a medium bowl, toss the chicken with the orange juice and 2 tablespoons of the olive oil and season with salt and pepper. Let stand for 10 minutes.
Meanwhile, brush both sides of the bread with the remaining 1 tablespoon of olive oil and grill until toasted, turning once. In a bowl, mix the mayonnaise with the parsley, cornichons, mustard, scallion, garlic, capers and lemon juice.
Grill the chicken over high heat until lightly charred and cooked through, about 6 minutes. Spread the remoulade on the toast. Top with the chicken, a few slices of lemon and the watercress. Close the sandwiches, cut in half and serve.