This classic French picnic sandwich is built on a crusty baguette loaded with fresh vegetables and bright flavors. The filling features pan-roasted asparagus, marinated heirloom tomatoes, crisp cucumbers, and a creamy herb dressing. It is an excellent handheld meal for an outdoor lunch or a relaxed weekend gathering. Briny olives and fresh basil add a punch of Mediterranean flavor to every bite. Wrapping the sandwich tightly allows the tangy red wine vinegar and dressing to soak into the bread for a rich, satisfying texture.