Combine lentils, water, and bay leaf in a pot and bring to a boil over high heat. Once boiling, reduce heat to medium-low, cover, and simmer for 16-20 minutes until the lentils are tender but still hold their shape—French green lentils should have a slight firmness to them. Drain the cooked lentils in a colander, discard the bay leaf, and spread them on a plate to cool to room temperature, about 10-15 minutes. I prefer French green lentils for this salad because they maintain their texture and don't turn mushy like brown lentils would.

While the lentils cook, prepare all your vegetables and herbs to have everything ready for assembly. Dice the cucumber into 1/2-inch cubes, finely mince the red onion so it distributes evenly throughout the salad, chop the dates into 1/4-inch pieces, and roughly chop the parsley. Chop the fresh mint and set aside separately. Having all your prep work done before you combine ingredients will make the final assembly quick and seamless.

Transfer the cooled lentils from Step 1 to a large mixing bowl. Add the cucumber, red onion, dates, and parsley from Step 2, then pour in the lemon vinaigrette and toss everything together until well combined. The warm lentils will absorb the vinaigrette beautifully, so make sure all components are evenly coated. Fold in the chopped mint and crumbled feta cheese gently at the end to maintain the texture of the cheese.