Prepare your ingredients and get your equipment ready, making sure to scrub your potatoes well. Preheat your oven to 180°C/350°F/gas 4.
Prick your sweet potatoes with a fork (once on each side), then, rub or brush with extra virgin olive oil. Now, sprinkle with a pinch of salt and pepper.Put the sweet potatoes on a baking tray, and bake in the oven for 45 minutes.
In a medium-sized bowl, add the remaining ingredients - tuna, yoghurt, sweetcorn, red peppers, spring onions (scallions), lemon juice, cumin, turmeric, and the remaining salt and pepper.
Mix everything together, cover and put to one side until the sweet potato jackets have baked.
After 45 minutes, the sweet potato jackets should be ready. To check, pierce with a knife - the flesh should be super-soft.
Split the sweet potato jacket open with a knife and fill with tuna. Serve with a side of salad.