If you’re capable as a kitchen whizz, you will be able to most likely do all all of these things at once and just serve up. But for those of you not as confident in the cooking space, cook your mash and veggies first and set them aside and then cook your steak OR cook your mash first and cook your veggies whilst cooking your steak. You can also your other half to cook the meat whilst you do the veggies and mash.