Preheat oven to 160°C and grease a baking dish.
Heat oil in a frying pan over medium heat and add onion, cook stirring often for 2 minutes or until soft, remove and place in a bowl.
Add sausages to frying pan and fry until cooked through, set aside to cool then slice.
Spoon sausages, onion, carrot, zucchini, and cheese over bottom of baking dish.
Whisk flour, dry soup, and milk in a bowl until smooth. Add eggs, and salt & pepper to taste, whisk until well combined. Pour over sausage and veggies in the baking dish.
Bake for 50 to 60 minutes or until set. Allow to rest for 5 minutes before serving.