Fry the leeks in a medium pan in the oil in a medium pan until soft. Add the garlic and cook for 5 minutes.
Ladle the leeks into a big ovenproof dish and top with the fish fillets and the chopped parsley.
Prepare the sachet of the Knorr Three Cheese Sauce as instructed on the packaging. Top with the mozzarella and bake in the oven for 12 minutes to bake and then under the grill for 3-5 minutes to get some colour.
Serve with fresh parsley, lemon wedges and Robertsons Black Pepper.