1. Add the lentils to a medium saucepan and add the water. Add one teaspoon of salt, the garlic, and the bay leaf and bring to a boil. Simmer over low heat for 10 to 12 minutes until almost tender. Turn off the heat and let sit for five minutes so they continue to gently cook. Drain, rinse, and set aside. Discard the bay leaf and reserve the garlic cloves.
2. Add the beets to the saucepan. Cover by two inches with water and add 1/2 teaspoon salt. Bring to a boil, reduce the heat, and cook at a lively simmer for about 30 minutes, or until a paring knife inserted into a beet meets no resistance. Turn off the heat and let the beets cool in the liquid for at least 10 minutes so they continue to gently cook. Drain and cover with cold water right in the pot. Slip the skins off under the water.
3. Meanwhile, in a small bowl, mash the reserved garlic cloves with a fork. Stir in the orange juice, vinegar, mustard, and the remaining 1/4 teaspoon salt and pepper. Slowly mix in the oil.
4. Cut the beets in half lengthwise (or quarter if large) and slice them about 1/4-inch thick. Mix with the dressing while they’re still warm. Stir in the lentils and adjust the seasonings. At this point, you can refrigerate for up to two days or proceed with the recipe. Bring back to room temperature when ready to serve and adjust seasonings to taste.
5. When ready to serve, toss with the arugula and the shallots.
6. Gently fold in the cheese and transfer to a serving bowl. Use a mandoline or a sharp knife to thinly slice the radish and strew over the top.
Notes: Small black beluga lentils, so named because they resemble caviar, can be used too, but avoid the more common brown lentils, which won’t stay firm enough for a salad when cooked.