Prepare the beets as directed. Chop the roasted, skinned beets into pieces that are about 1" (or a little smaller).
Bring a pot of water to boil. Drain the lentils of their soak water, then add them to the pot. Reduce the heat to medium low and simmer the lentils for 25-30 minutes, or until they're tender but still hold their shape. Drain the lentils, taking care to remove as much cooking water as possible so that they're not watery when you add them to the salad.
Add the prepared beets, lentils, and a half cup / 120ml of the dressing to a large mixing bowl. Toss to combine. Add the baby arugula and chives. Toss again, gently. Taste the salad and continue to add dressing as needed, until it is well-dressed but not soggy.
Serve the lentil beet salad with your favorite toast or bread.