Preheat oven to 350° F and grease a loaf pan with butter.
In a small pot, add lentils, water, and 1 tsp salt. Bring to a boil, reduce the heat, cover, and simmer for 25-30 minutes or until lentils are tender.
Add cooked lentils to a medium mixing bowl and add oats, cheese, and onions and mix until combined. Add the remaining ingredients and stir until completely incorporated.
Pour mixture into greased loaf pan and bake for 30 minutes.
Meanwhile, mix together the topping in a small bowl by combining the ketchup, balsamic vinegar, and brown sugar. Pour on top of the 'meatloaf' and cook for an additional 10-15 minutes.
Let rest for 10 minutes and then serve and enjoy!
