Play the mission where you fight the giant Knight at the Vex relic on the Level 12 Heroic. If you're L25+ you won't die when you melee them. Just do them one at a time and wait for your health to fully regenerate before going for the next one. I did it in one pass of the mission. Add a few bounties from Eris / Vanguard, pop a few Hive Glimmer boosts and make it a more worthwhile run!