Cook the farro according to package directions. I used a quick-cooking (10 minute) Italian farro, but other varieties may take up to 50 minutes. When the farro is done, strain any excess liquid, and return farro to the pot. Sprinkle with salt, stir, and allow to cool for a few minutes.
Rinse and sort the lentils.
To prepare the lentils in an Instant Pot, combine all ingredients in the IP insert. Lock on the lid, and set to sealing. Cook at high pressure for 10 minutes, then quick release remaining pressure. Carefully remove the lid, and check the texture of the lentils. I prefer lentils on the firm side for salads, but if you prefer them softer, re-secure the lid and cook for an additional 1 to 2 minutes. When done, strain the lentils and discard the liquid. Return lentils to the pot. Remove lemon peel, mash the clove of garlic against the side of the pot, and stir it into the lentils. Set aside for a few minutes to cool.
To prepare the lentils on the stovetop, combine all ingredients in a soup pot. Bring to a boil, then cover, reduce heat to low, and simmer for 20 to 25 minutes or until lentils are as tender as you like. Strain the lentils, and return to the pot. Discard the lemon peel. Smash the garlic clove against the inside of the pot, and stir to distribute. Set lentils aside for a few minutes to cool.
Make the dressing. Combine dressing ingredients in a bowl, and whisk with a fork until smooth. Set aside.
Assemble the salad beginning with a bed of arugula, then arrange the farro and lentils. Top with cucumber, onion, tomatoes, cilantro, and feta. Serve with lemon wedges and dressing on the side.
For meal prep, store each component separately, then briefly warm the farro and lentils before assembling the salad (this is mainly for food safety but also tastes better than cold). If you've already assembled a large amount of salad and have some leftover, it will keep for a day or two. Store dressing separately.*Lentils adapted from Lentil Eggplant Salad by Recipe Tin Eats.*Nutrition facts are an estimate and will vary based on exact amounts of dressing and cheese used.