Place the lentils in a saucepan with the onion, thyme, bay leaf, and water. Cover and bring to a boil. Lower the heat so that the water boils gently. Cook, covered, until the lentils are tender but not mushy, 30 to 40 minutes (the timing can vary).
Drain the lentils; discard the liquid and aromatics (onion, thyme sprigs, bay leaf). Season the lentils with salt