Preheat the grill to high. Cook the macaroni following the instructions on the packet, adding in the broccoli for the last 3 minutes.
Meanwhile, heat the oil in a large frying pan and cook the onion for 5 minutes until golden. Add the bacon and cook for a further 5 minutes.
Stir in the flour, then add the soft cheese, milk, sweetcorn, cooked pasta and broccoli. Cook gently for 2-3 minutes. Season with freshly ground black pepper and pour the mixture into a one-litre ovenproof dish.
Mix together the cheddar, breadcrumbs and parsley, and sprinkle evenly over the macaroni. Cook under the grill for 5 minutes until golden and bubbling. Serve with the lettuce and tomatoes.