I never ate lentils until I was in college but I’m doing my best to make up for lost time. In France (and I’m guessing elsewhere in Europe) people eat a lot of lentils, both warm and cold. A very typical salad in the summer is a cold lentil salad.
The video shows one recipe but really, you can add or subtract options as you like. Instead of scallions I tend to use shallots and while I’ve never added egg (sounds like a good option) I’ve added feta cheese. If you can’t locate good tomatoes, you might try chopped cherry tomatoes which will give a nice flavor. I also add either a touch of vinegar or lemon juice to the olive oil but add what you like.