To prepare the marinade, mix the lemon juice, mustard, garlic, salt, and pepper, in a big bowl. Pour in the olive oil slowly while stirring so it mixes well.

Put the chicken pieces in the marinade bowl making sure all the pieces are coated. Cover the bowl and refrigerate for at least 2 hours.

Transfer the marinated chicken with the remaining marinade to an oven tray, and place in a heated oven. Flip the chicken over to cook on both sides. If it gets too dry, add some water and lemon juice.

When the chicken is done, take out from the oven and leave to cool then slice into strips.

To prepare the sauce, mix the chopped parsley with the mayonnaise, in a small bowl then stir in the lemon juice.

Toast the opened sandwiches a little then generously spread sauce inside. Put the shredded lettuce over the sauce followed by the chicken strips, and then close the sandwiches.

Serve slightly warm.