Chop corned beef into smallish cubes, about a centimetre should be enough. Chop potatoes into flat discs and cook in a pot of water, insure the potatoes don't get too soft.
Fry off bacon and onions until golden. Add tinned tomatoes, corned beef and the beef stock. Add some water if the stock is a cube, and allow to simmer. Allow the mix to simmer until the mixture is less watery, but not too thick.
Remove the potatoes from the water and place them onto a tea towel, to remove some of the water. Pour the corned beef mix into a casserole dish and add a layer of baked beans on top.
Lay the potatoes on top of the tray in a roof tile formation and sprinkle a layer of cheese on top. You can also add salt or pepper to the top if you would like.
Cook in an oven at 220 C / Gas 7 until golden, between 30 and 45 minutes.
You can glaze the potatoes in oil to create a crispy top. Herbs are good too!! Add some thyme, rosemary or a few sage leaves to the mix whilst the mixture is cooking in the pot.