Preheat the oven to 180 C / Gas 4. Grease an ovenproof casserole dish.
In a frying pan, melt the butter then add the potatoes and cook for 5 to 8 minutes, browning slightly. Arrange the potato in the base of the prepared casserole dish and pour over the stock.
In the same frying pan, heat the oil. Add the onion, leeks, garlic, seasoning and spices and cook and stir until soft, about 5 minutes Add the sundried tomatoes and heat through. Spoon half of the vegetable medley into the prepared baking dish over the potatoes. Layer the mozzarella cheese on top then cover with another layer of vegetables. Place the sliced Red Leicester on top.
Bake in the preheated oven until the potato is soft and the cheese melted and golden brown, 45 to 55 minutes. Remove from the oven and serve.