Hiya!

Sounds like you have most of what you need!

Brown off mince with some finely chopped onion, add some frozen veg. Season with pepper and salt to taste. Splash in some worcestershire sauce...finish off with some gravy powder ( mixed into a paste. Stir to thicken...

You can add tomato purée or some chilli if you want. Also grated carrot, zucchini or mushrooms...if it needs a lift of flavor, stock powder can help (teaspoon or two)
Put in casserole dish and top with mashed potato (I like to put some cheese in mine)

Brown in oven.

Hope this helps!!