· Preheat oven to 180 degrees C. Grease 20x30cm baking dish.
· Melt margarine in a medium saucepan. Remove from heat then mix in the flour and milk. Return to stove over medium heat and stir until thickened. Season with salt and pepper.
· Flake tuna into baking dish alternating layers with sauce. Sprinkle top with grated cheese and corn.
Bake in preheated oven for 20 to 25 minutes or until cheese is browned.