Whiz the onion, carrots and broccoli stalks in the food processor until they are a fine pulp.If you are using fresh bread add the bread slices a little at a time the veggie mix and whiz them until they are tiny crumbs and well combined. If using packaged breadcrumbs add them to the veggies and mix well.Add the veggie and bread crumb mix to the minced meat along with the egg and herbs and mix well, you might need to use your hands to get a nice even mix. If the mixture is too wet add the flour a table spoon at a time, and/or more breadcrumbs until the mixture comes together and rolls well into balls.Line a large tray with non stick paper and place the rice into a small dish. Roll spoonfuls of the meat mixture into tight balls, coat with a little rice and place them on the tray.Continue until you have a tray full of rice covered meatballs, make sure they are not touching each other, then cover with plastic wrap and pop them in the freezer for an hour or so, or until they are well frozen on the outside.Once frozen put the meatballs into a sealed freezer bag and place into the freezer until needed.To cook the meatballs - grease a large baking dish (preferably one with a lid) and pop in as many frozen meatballs as you need.Make up enough tomato soup to fill the dish and cover the top of the meatballs.Place the dish of meatballs into the fridge for a few hours until you are ready to cook them, or add approx 45 minutes to the cooking time.Cook the meatballs in a moderate oven, with the lid on, for at least 1.5 hours, or until they are cooked through and the rice is soft, adding more liquid if needed.