Peel and chop the sweet potato into chunks. Boil in some slightly salted boiling water for about 15 minutes until tender, then drain and mash.
Drain the tuna and sweetcorn and put them in a bowl along with the warm, mashed sweet potato.
Season with some black pepper and mix well.
Pre-heat the oven to 200oC/400oF/Gas Mark 6.
Make some breadcrumbs with the sliced bread.
Put the breadcrumbs in one bowl and the flour in another.
Whisk the eggs in a bowl.
With a dessert spoon, divide the tuna mixture into 12 balls. Dip them in the flour first, then the egg and then the breadcrumbs.
Fry them in batches in some oil until golden all over.
Transfer to the oven to keep warm.
Meanwhile, cook the vegetables in some slightly salted boiling water for about 7-9 minutes.
Drain and serve the vegetables alongside the fish balls.