Place carrots, potato and onion in the slow cooker. Pour in tomatoes and crumble in 1 to 2 stock cubes, to taste. Season with salt, pepper and herbs of your choice. Add water to cover. Cover slow cooker and cook 4 to 6 hours on High, till veg is tender.
At the end of cooking, add the tin of corned beef. Stir and warm through, then serve.