2) In a bowl, add the lemon juice, caster sugar or honey, parsley, garlic and extra-virgin olive oil. stir to combine. Season the chicken with salt and pepper and add to the dressing, turn to coat and let marinate for 15 minutes.
3) Heat a large skillet or griddle pan. Shake off excess marinade and cook the chicken for 6 minutes on each side. Remove to a cutting board, let rest for a few minutes and slice on an angle.
4) While the chicken marinades and cooks, add the butter to a sauce pot over medium heat. When the butter melts, stir in the plain flour, cook 1 minute, then whisk in the stock. Cook until thickened to a light gravy, about 5 to 6 minutes. Season with black pepper, remove from the heat and stir in the Dijon mustard.
5) While the chicken cooks, crisp the bread in the warm oven. Cut the bread into 4 portions and split or halve. Use tongs to dip the sliced chicken in the gravy and fill the rolls. Arrange on a serving platter and serve.