"find a crop" has already been done on Earth, the more appropriate need is to find a successful crop at 1/3rd gravity.   Realistically speaking any of the cereal grain or wheat crops will, in a ~50x50 foot flat space produce enough carbs for a years life.  If you use wheat you are looking at an 18 to 24 month cycle of harvest but with barley you can be on a 2 month cycle.  Millet would also be valuable to attempt as well,  they have a longer grow to harvest than barley but they don't need a lot of water resource.  Bring in quails, bring in society finches, bring in angora rabbits and you begin to build an ecosystem that provides not just digestive nutrient transformation but meat, eggs, feathers and fur each of which go to supporting the human life cycle.