It is a good idea. Lentils are super cheap. I'd use black or green, not red, for this. Cooking them in stock with seasonings would give them more flavor. Keep an eye on them because you'll want to strain them before the get mushy. I can't think of a reason steaming would be preferred to simmering here, though, so that's what I'd do. They freeze well, so you can make a big batch and freeze individual portions.