Cook the lentils for 20 minutes (starting from cold) and let them cool.
Preheat the oven to 200°C (thermostat 6-7).
Peel and grate the carrot.
Finely chop the onion and sauté it in the pan with olive oil.
After 5 minutes add the carrot and cumin.
Let it simmer.
In a bowl, crush the lentils with the tomato paste.
Add the onion/carrot mixture, the egg, the breadcrumbs, salt and pepper. Mix well.
Form into patties and place them on a baking sheet lined with parchment paper.
Bake for 30 minutes and turn over halfway through cooking.
Toast the burger buns.
Spread mayonnaise on the buns, add a lettuce leaf, a lentil patty, and a piece of cheese. Close the burger with the bun, which has been brushed with ketchup.