Brown your meat in a skillet, add in your veggies - onion, peas and carrots.
Your onion and carrots need to soften, although 100% cook does not need to be accomplished in the skillet, as you're going to be putting the completed dish in the oven or under a grill (if using a grill only to brown the mash, cook longer in your skillet).
Crumble in your oxo-cubes, add your Worcestershire sauce and if the mix is dry, a splash of water. Your veggies will release liquid, so do not over-do the water at this point.
Stir and adjust your meat mixture to taste with S+P to your own tastes.
Cube, then boil and drain your potatoes and make up your mashed potato as you like it. We add about a stick of butter and some white pepper to "pep-up" the mashed potato. If needed, add a little milk, but do not make your mashed potatoes too "wet". On the flip-side, you need to be able to flatten, spread and make patterns in the top of your mashed potatoes, so don't make them too stiff... think Goldilocks and potato stiffness, one was too-wet, one was too stiff... this one is "just riiiight..." :)
Simmer your meat mixture for at least 20-30 minutes. I tend to put mine on REALLY low and let it cook for close to an hour - adjust your seasoning and remember that when consumed with potato, the mixture spice-level will be "muted" - so don't overdo the spice, but err on the side of a little more. Lea & Perrin's Worcestershire sauce is the flavour booster...
Let the meat mixture cool somewhat before assembling your dish. Our ideal ratio is an inch and a half of meat mixture to about an inch and a quarter of mashed potato.
Make diagonal lines with a fork in your mashed potato mixture and finally outline the whole dish with a few scores around the perimeter.
Put the mixture in a 350f oven for 20 minutes or so, and finish under the grill to brown the top.
Remove from the oven and let sit for 10-20 minutes and serve.