Preheat your oven to 360°F.
Put the lentils, buckwheat, rolled oats in a large saucepan, add the water, bring to a boil, then reduce the heat to low and cook for 20 minutes, until the water has been absorbed.
Put the previous mixture in a salad bowl, add the other ingredients, salt and pepper then pour into a previously oiled cake mould
Bake in the oven for 50 minutes to 1 hour.
Meanwhile, prepare the sauce. Heat the olive oil in a saucepan, add the shallot and the mushrooms, cook for 5 minutes.
Add the vegetable broth, tomato puree, thyme and bay leaf, cook over high heat until reduced by 1/3. Add the diluted starch and the red wine. Let thicken.
Serve the lentil roast with the sauce and enjoy!