Preheat oven to 180°C.
Arrange half the sliced potatoes in a greased, ovenproof dish.
Open the tins of tuna and drain the liquid.
Spread evenly over the first layer of potatoes and top with layers of sliced tomatoes and the remaining potato.
Season with KNORR Aromat and pepper.
Mix the KNORR Creamy Garlic and Herb Potato Bake sachet contents with a little milk to make a paste and stir in the remaining milk.
Pour over the potatoes, sprinkle with cheese and bake at 180°C for 1 hour until the potatoes are soft and the cheese is golden brown.