Preheat the oven to 180C
Place the sweet potatoes on the stove to boil until soft
Fry the chopped onion in the olive oil until soft
Add the baby marrows and carrots and fry for an extra 5 minutes
Add the mince, Worcestershire sauce, tomato paste and allow the mince to cook
Add salt and pepper to taste
Once the sweet potatoes are soft, drain the excess water and puree using a stick blender or mash by hand.
Add the milk, margarine and salt to the mashed potato
Layer the cooked mince in an oven proof dish and cover with the mashed sweet potato
Bake in the oven for 30minutes