Preheat the oven to 200c/400f. Place the romano peppers on a baking tray and drizzle on 1 ½ tbsp of the olive oil, then rub the oil all over both sides. Arrange on the tray cut side up and sprinkle on a pinch of salt and pepper. Place in the oven to cook for 15-20 minutes until the peppers are soft and slightly charred at the edges.
Meanwhile heat the remaining ½ tbsp oil in a small sauce pan. Peel the red onion and cut it in half. Cut one half into thin slices and put to one side. Chop the other half finely into small pieces. Place the small pieces into the pan and cook on a medium heat for 5 minutes until the onion softens. Add in the peppers, garlic and oregano and cook for a further 2 minutes, then stir in the couscous. Add the vegetable stock, bring to the boil, then turn off the heat and place a lid on the pan. Leave for five minutes to cook, then remove the lid and fluff with a fork. Season to taste.
Slice the cucumber in half lengthways and scoop out the seeds using a teaspoon. Slice in half lengthways again, then cut into quarter-moon pieces.
Make the dressing by mixing all of the dressing ingredients together in a small bowl using a fork.
Arrange the mixed leaves on a large serving dish. Place the cooked peppers on top. Stir the parsley and basil through the couscous, then use a spoon to stuff the peppers with the couscous. Crumble the feta cheese on top of the peppers, then scatter the red onion slices, sliced olives and cucumber slices over the top of the dish. Serve immediately with the dressing.