Preheat the oven to 250 degrees Celsius.

Cut the tops off the burger buns and hollow out the insides, being careful not to damage the buns.

Set the bun tops aside.

In a pan, combine ground beef, lentils, chopped celery, chopped onions, chopped capsicum, and any optional ingredients (eggs, raisins, carrots).

Cook until the meat is browned and the onions are transparent.

Fill the hollowed-out buns with the meat mixture, packing it in tightly.

Optionally, add egg whites to help bind the filling.

Top with sliced cheese and then the reserved bun tops.

Place the filled buns into the preheated oven.

Bake until the bread is crispy and the cheese is melted.

Serve with salad or chips.