Preheat oven to 180°C.
Heat margarine and oil in a pot and gently fry onion and garlic until tender.
Add button and brown mushrooms and fry until soft.
Add the sweet potato, chopped tomatoes, KNORR Creamy Mushroom Sauce and milk and stir until well combined.
Bring to the boil, reduce heat and allow to simmer for 15 minutes with the lid on, stirring occasionally.
Transfer to an oven-proof casserole dish, top with grated Parmesan and allow to bake in the oven for 20 minutes or until the sweet potato is soft and cooked through.