Preheat the oven to 200C/Gas 6/fan oven 180C. Cut the peppers in half through the stalks and scoop out the seeds. Put the peppers in one layer on a baking sheet. Drain the mushrooms, reserving the oil from the jar – drizzle one tablespoon of the oil over the peppers, then sprinkle with salt and pepper. Bake for 20-25 minutes, until the peppers are just tender.
Tip the couscous into a bowl and pour in the hot stock. Leave for 5 minutes to soak, then fluff up with a fork and stir in the mushrooms, halloumi and parsley. Season with salt and pepper and spoon into the pepper halves. Return to the oven for 15 minutes, until the cheese is golden. Serve the peppers warm with a mixed salad and garlic bread.