In a large saucepan, combine the water, lentils, carrot, onion, garlic, and bay leaf. Season with salt and pepper. Bring to a boil. Lower the heat and simmer, partially covered, until the lentils are soft, 15 to 20 minutes. Drain, discarding bay leaf.
Use a paper towel to wipe out any water from the saucepan. Add oil, and return pan to medium heat. Stir in the lentils, vegetables, and spinach. Cook, stirring occasionally, until the spinach is wilted, about 2 minutes. Taste, and adjust for seasoning. Use a slotted spoon to transfer to serving bowls.