Enviousamerican: No, my mum didn't drain the tomatoes, because the juice added the ''gravy' to the mushroom/onion mix that was then served with rice.
She made the shepherds pie as Annsixty mentions: with onion and oxo (adding water too to make it moist - in fact, I personally used to use quite a lot of water then thicken with flour too! However, unlike Annsixty, my mum didn't layer the potato and meat, though that does sound like a great idea!
Lam64: I often used to make corned beef, onion and potato pie myself, back in the days when corned beef was way cheaper than the tinned stewed steak that my mum and grandma always used for meat and potato pie. Actually, I haven't had that for years - it might go on next week's menu 