Cook the rice in lightly salted boiling water for about 15 minutes until tender or according to the instructions on the packet. Add the green beans for the final 2 minutes of cooking. Drain and set aside.
Meanwhile, heat the oil in a large frying pan and cook the onions gently for about 12 minutes or until soft and golden. Add the balsamic vinegar and thyme, season with salt and pepper and allow to bubble gently for 2–3 minutes until the mixture thickens slightly.
Stir the onions into the rice and beans and leave to cool. Once cool, scatter over the cheese, tomatoes and basil leaves and serve.