Put the olive oil, lemon juice, tomato puree, vinegar and chives in to a large bowl and whisk together until thoroughly blended. Cook the thin green beans in lightly salted boiling water for 4 to 5 minutes until cooked. Drain, refresh under cold running water and drain all water.
Add the green beans, soya beans and red kidney beans to the dressing, stirring to mix together. Add tomatoes, spring onions and feta cheese to the bean mixture, tossing gently to coat in the dressing. Season the salad with salt and pepper.