For the tuna-rice salad, first steam the rice until soft and then let it cool.
Add the cut tuna, the halved onion, the diced gherkins and the mayonnaise. Then season to taste with the spices.
Put the mixture in a bowl and let it sit in the refrigerator for a day.
The next day, place lettuce leaves on a serving platter, turn the tuna-rice mixture onto it and garnish with eggs, tomatoes and gherkins.