Chickens are my favorite/easiest keto vegetables to grow.
But you might try:
Swiss chard, leaf & romaIne lettuces, collards, mustard, kale and turnip greens, radishes, spinach, sage, basil, parsley, cilantro, green onions, sorrel and stevia
My preference is for things that can be continuously harvested in small quantities - pretty much all the leafy vegetables and herbs, which also tend to be the most keto friendly. As for soil, it doesn’t matter much what you start with for small garden plots because you can/must amend it with the addition of lots of organic matter: manure, leaves, composted kitchen waste, etc. Bordered or raised beds can speed the process of creating fertile soil.