Drain the liquid from the corn.
Strain the brine from the beans into a bowl.
Add olive oil, sugar, soy sauce and lemon juice to the strained brine. Stir until the sugar dissolves and adjust the taste if necessary.
Cut the onion into thin half-rings and put it in the marinade.
Allow to marinate for 15 minutes.
Put the string beans in a salad bowl, put the corn and onion on top.
Pour the dressing in which the onion was marinated.
When serving, sprinkle the salad with sesame seeds.