This is as basic as basic can be, when Storm Rising is available, play the All heroes version on Hard Difficulty. If you are playing with a group this is easy as you can basically have 2-1-1 set up (2 Damage 1 Tank 1 Support or 2 Tank 1 Damage 1 Support) and just march on through. I do advise using Orissa as the tank, not only can she eat the charge of the Heavy, she can also group enemies together and provide shielding if everyone plays at a distance
If you are playing with randoms... well... you probably going to end up being either the Tank or Support. For whatever reason unlike on PC, randoms on the Xbox version of Overwatch pretty much refuse to do either role for Storm Rising.