Preheat the oven to 180C.

Heat oil in a large saucepan over medium heat. Add the onion and celery to the pan and sauté for 5min until it begins to soften. Add the butter to the pan and melt, then stir through the flour until the mixture is completely coated. Gradually pour in the milk, stirring to avoid lumps forming. Bring to a gently simmer for 5-10mins as it begins to thicken then stir through the tuna, corn and season with salt and pepper.

Pour into a baking tray and top with breadcrumbs and cheese. Bake in the oven for 20mins until golden and brown.

Serve with pasta or brown rice.