Put the green beans, kidney beans, white beans and corn in a large bowl and mix well.

Halve the red onion and cut into fine rings. Chop the parsley and add to the bean mixture together with the onion rings.

Halve the cherry tomatoes and add to the ingredients.

For the dressing, mix the white wine vinegar with olive oil, salt and mustard until everything is well combined.

Mix the dressing into the salad and serve.