Slice cucumber and carrot into thin strips, and shred cabbage using a potato peeler.

Place the sliced vegetables in a bowl and add 1 tbsp sugar, 2 tbsp vinegar, 0.5 tbsp salt, and a pinch of ground pepper. Let them marinate for 30 minutes to 1 hour.

After marinating, squeeze out the excess water from the vegetables and discard the liquid.

Mix the marinated vegetables with 5 tbsp mayonnaise until well combined.

Cut the morning bread in half.

Fill the bread halves with the prepared vegetable mixture and add ketchup on top.