Add lentils to a saucepan. Cover generously with water. Bring to a boil and cook for about 20 minutes, until soft. Drain and set aside.
Preheat oven to 425°F. Line and grease a baking sheet. Add beets and sprinkle with salt; spray with cooking spray. Bake for 15 minutes.
In a bowl, combine lentils, beets, lemon juice, parsley/cilantro, and salt. Keep in an airtight container in the fridge until ready to serve. Can be made up to a couple of weeks ahead (but I don’t know if that’s advisable because then you’ll eat it before the time you were planning on serving it…because that’s what happens when there’s something filling, healthy, and ready-to-go in the fridge).