Preheat the oven to 195°C.
Cut the zucchini in half and make two as large as possible rectangular pieces by cutting as little as possible. Season with pepper and salt, brush with olive oil, and coat all around with sesame seeds.
Place the zucchini on a baking sheet lined with parchment paper and bake for 25 minutes in the preheated oven.
Toast both slices of bread in the oven or toaster and spread mustard on both sides.
Fold the cheese in half so it fits on the toast. Place the zucchini steaks, grated carrot, cressonette, and the other toast on top.
Wrap the sandwich in butter paper and cut it in half so the beautiful layers are revealed.
Tips
Let the sandwich cool first before you take it to work in a closed bread box, so that it does not become waked. You can also replace the zucchini with eggplant and prepare it in the same way.