Preheat the oven to 180°C/ 350°F/Gas mark 4.
Drain the salmon, reserving the juices. Cook the macaroni in salted boiling water until al dente, drain and transfer to a deep casserole dish. Mix in the salmon.
In a bowl, mix together the sweetcorn, tomatoes, onion, celery, soup and lemon juice. Season with salt and pepper, and pour over the salmon mixture. Bake in the oven for 30 minutes. Serve hot.