Heat the broiler to high. Place the mushrooms gill-side up on a rack, brush all over with with the oil and season with salt and ground black pepper. Cook under the broiler for 5 mins until the juices start to run.
Top with the halloumi cheese slices then return to the broiler and cook for a further 4-5 mins until the cheese is golden and crisp.
Arrange the mushrooms on serving plates and spoon a little chili sauce over each. Serve with the salad leaves.