Put the 500g of turkey mince, 1/2 cup breadcrumbs, 1/2 finely chopped onion, 1/2 cup of grated parmesan cheese, and the beaten egg into a large bowl.
Mix well and season with salt and pepper.
Roll into small balls and put these into the base of the slow cooker and cook for 1.5 hours on high.
Turn the meatballs over carefully with tongs to make sure they will cook evenly.
Then add the rest of the finely chopped onion and can of tomatoes, and season with salt and pepper.
Cook on high for 3.5 hours
Finally, add a handful of grated cheese over the top and cook for another 1/2 hour or until the meatballs are cooked and the cheese is golden.
I served them with rice.