Heat the oil in a small pan and fry the potato for 3-4 minutes until soft and caramelised on the edges. Add the garlic, onion, tomato, cumin seeds, and seasoning, and cook for 1 minute. Remove from the heat and leave to cool slightly.
Preheat the sandwich toaster to its highest setting.
Brush one side of one slice of bread with olive oil and place in the sandwich toaster oiled side down. Cover the bread with the potato mixture and sprinkle over the cheese and basil. Cover the sandwich with the second slice of bread and brush the top of the sandwich with more olive oil. Carefully close the lid and cook for 5 minutes until crisp and golden.