Bring vegetable stock to a boil. Measure couscous into a large salad bowl or serving bowl. When vegetable stock boils, pour over couscous, stir, then place a large plate on top of the bowl and set aside for 5 minutes.
In the meantime, chop the veggies.
Fluff the couscous with a fork, then add tomatoes, sliced onion, diced peaches, lemon juice, olive oil and a pinch of salt and pepper to the bowl and toss to combine. If making ahead or time, transfer to a container with a tight fitting lid at this stage and place into the refrigerator. And then, proceed with the next steps just before serving.
When readt to serve, add arugula, avocado and basil and toss to combine. Serve.