Mixing small amounts of complete proteins with lentils will provide you with a complete source of amino acids. Most plant sources of protein are incomplete, with the exception of soybeans and quinoa, but animal sources of protein including dairy products, meat, fish, poultry and eggs are complete proteins.onsider making a salad with both lentils and some type of nuts. You can use lentils in a Waldorf salad, for example, to make it a meal with complete protein.