Preheat oven to broil. In small bowl whisk cornstarch with 1 cup (250 mL) water until smooth; set aside. Heat oil in large saucepan over medium heat. Add celery and onion; cook 5 to 7 min. until soft. Stir in cream and bring to a boil. Whisk in cornstarch mixture. Let bubble about 1 min., or until thickened. Add tuna, peas and pasta. Cook about 4 min., or until heated through.
Pour pasta mixture into 13 x 9-in. (3-L) baking dish. Sprinkle cheese over top. Broil in oven about 3 min., or until sauce is bubbling and cheese is melted.
This dish travels well. Simply reheat in the oven or microwave until warm.
Make this dish dairy-free by substituting vegetable or chicken stock for the cream and substituting 1/2 cup (125 mL) gluten-free breadcrumbs for the cheese.