1. In a small saucepan, melt the butter and sauté the spring onions. Add the flour and stir for 1-2 minutes. Gradually pour in the milk, stirring continuously with a whisk until the sauce thickens.
2. Remove from heat and add: the tuna (flaked), corn, carrot, lemon zest, parsley, mustard, cheese, and salt and pepper. Mix well until you have a homogeneous, firm filling.
3. Place the mixture in the refrigerator for at least 2 hours or until firm (ideally overnight). In 3 separate containers, place the flour, beaten eggs, and breadcrumbs.
4. Shape into elongated croquettes or small balls and coat them first in flour, then in the beaten eggs, and finally in the breadcrumbs.
5. Heat oil over medium heat and fry until evenly golden brown on both sides. Place on absorbent paper. Alternatively, bake in a preheated oven at 200°C (fan-assisted) for 20-25 minutes, after drizzling them with a little olive oil.
