Bring the water to a boil in a kettle. In a measuring cup, mix the hot water with the vegetable stock powder, tomato paste, light balsamic vinegar, sunflower oil and erythritol with a whisk.
Put the green beans, kidney beans and corn in a salad bowl. If you like, you can rinse the ingredients in a sieve beforehand. Pour the dressing over the ingredients and stir in.