Soak onions in cold water for at least 10 minutes to remove the bite and mellow out the flavour of raw onions.
Combine all ingredients for the vinaigrette. Stir well to combine and set aside.
Prepare a bowl of ice-cold water to shock the green beans. Steam beans until tender but still crisp, about 3-5 minutes. Immediately plunge into the water to retain colour and stop the cooking process. Drain and set aside.
Heat a greased cast-iron skillet over medium-high heat. Grill the halloumi and peach wedges, flipping after 3-5 minutes until both sides are nicely browned. Combine the cheese and peaches with the rest of the ingredients. Drizzle vinaigrette and gently toss to combine. Enjoy!