Lately we have been replacing ground hamburger for lentils (or you can do half and half). As long as you add seasoning to the lentils it usually tastes great, if not better than the ground hamburger. Remember to only cook the lentils until they are just done or else they will become soggy/mushy. We've done this very successfully with:
I season the lentils with taco seasoning or I add chili powder, cumin, salt and pepper, onion and garlic powder, crushed red pepper flakes and maybe some oregano and paprika.
-Stuffed green peppers
I season the lentils with lots of salt and pepper, oregano, basil, garlic, onions, and tomatoes and mix it with rice and an egg or two.