Boil potatoes till tender and then mash as usual, seasoning with salt and pepper. Add butter and sufficient milk to make it fluffy and nice.
Preheat oven to 200degrees celsius.
Brown meat in a pan and drain it of excess juices. Transfer browned meat to a bowl.
Heat some oil in the pan and fry onions till tranluscent. Add in frozen mixed vegetables and cook till everything has warmed up. Add in salt, pepper, oregano, rosemary, canned tomatoes and mix. Add flour in and mix well.
Return lamb or beef to the mix. Simmer, uncovered, for around 25 minutes till the liquid has reduced by half.
Spoon meat filling into casserole dish. Top off with mashed potatoes and use a fork to score patterns on top.
Bake in oven for 20 minutes till potatoes brown nicely. You might want to switch to top grill in the last 7 to 8 minutes.