1.Place couscous and crumbled stock cube in a heatproof bowl; stir in 1 cup boiling water. Cover with plastic food wrap; set aside for 5 minutes or until liquid is absorbed. Using a fork, fluff and separate grains. Add onion, cannellini beans, tomato and dressing; toss to combine.
2.Meanwhile, melt garlic butter in a large frying pan over high heat. Add mushroom and green beans; cook and stir for 3-5 minutes or until soft. Remove pan from heat. Stir in parsley. Season.
3.Serve mushroom and green beans with couscous mixture.
Use 2 chopped regular tomatoes instead of cherry tomatoes. Make ahead: Make couscous up to 3 hours ahead. Cover, then refrigerate.