Clean the Lentils: Measure the lentils into a strainer or colander and thoroughly rinse under running water. Transfer the rinsed lentils to a saucepan and pour in the water and add the bay leaf.
Cook the Lentils: Bring the water to a rapid simmer over medium-high heat, then reduce the heat to maintain a very gentle simmer. Cook, uncovered, for 20-30 minutes. Add water as needed to make sure the lentils are just barely covered. Lentils are cooked as soon as they are tender and no longer crunchy. Strain the lentils and remove the bay leaf. Place the lentils in a bowl and add salt and let cool slightly.
Make the Salad: Add cucumber, onions and parsley to lentils. Whisk together apple cider vinegar and olive oil and drizzle over lentils. Toss and serve.