Basically what you have is what I'd use too. Brown mince and onion (I sometimes put in garlic too). I swig in a bit of soy sauce, tom paste or sauce, a teaspoon or two of chicken stock powder or a packet of chicken noodle soup mix. Then I toss in the frozen vegies and enough water to wet it all nicely and let it simmer till it thickens up nicely.
Obviously put the potatoes on to boil first - I like a cheesy crust on top so sprinkle over grated cheese before putting in oven and letting brown.