Its actually a pretty cool Bungie inside joke. The Steaktacular Medal is earned and achieved by winning an online matchmaking game with a score of 20+ points/kills more than the opposing team.
The history behind this medal is, The description, 'Luke owes you a steak dinner.', comes from a Bungie Hump Day Challenge where a a steak dinner was wagered, in which Luke Smith bet that he could beat another team, led by Frankie, by at least 20 points. Luke won 50-2. Thus Steaktacular.