That's a quick turnaround! I think of a few things right off the bat: First and foremost is kale, because it grows reasonably quickly and it's pleasant to eat at any stage, from mini to maxi. Lettuces are another good contender. In North America black-seeded simpson is a standard quick lettuce. You'll probably have different options but lettuce = quick greens. Another thing that comes to mind is turnips because they are -- or can be, anyway -- resilient, competitive, and quick and the greens are very edible.