Pre-heat the oven to 180C / 355F, then roast the tomatoes and corn on a baking tray for 10 minutes.
Meanwhile, heat the oil in a large frying pan, then add the halloumi cubes. Let cook for two or three minutes without moving, then toss and let cook for a minute or two longer. Repeat until the cheese is well browned and crispy. Drain on kitchen paper.
When cooked, tip the tomatoes and corn onto a large plate or platter, then add the cucumber, avocado and onion. Stir through the basil, then scatter the crispy halloumi over the top.
Whisk together the dressing ingredients in a food processor or blender. Serve the warm salad immediately, with the dressing on the side.