Because this food contains both legumes and grains, it is a complete protein, providing all the amino acids the body needs, the same way real meat loaf would.
Preheat oven to 350 degrees Fahrenheit. Grease a loaf pan.
In a medium saucepan, boil lentils in three cups water until soft. (This may take half an hour or more.) Strain.
Remove lentils to a mixing bowl and mash. Add onions, oats, cheese, egg, tomato sauce, and seasoning. Spread in prepared pan.
Bake for 30-45 minutes, or until the top of the loaf is dry, firm, and golden brown.
Cool for a few minutes before slicing.
You can replace the grated cheese with an equal amount of barbecue sauce. (I prefer the cheese-based dish.) This “meat loaf” can be served as is, or topped with a (mushroom) gravy or white sauce.