Heat a large saucepan; add the oil and sauté the vegetables until softened. Stir in the tomato puree then add the lentils. Cover with the vegetable stock and simmer until tender.
Steam the diced potatoes until just tender, refresh under cold water. Meanwhile, melt the Flora in a pan, add the crushed garlic, leeks and thyme, cook until leeks are softened. Stir in flour and cook for thirty seconds, gradually add milk to make a smooth béchamel sauce then add the potatoes, check seasoning.
Spoon the vegetable mix into a suitable baking dish, spoon over the potatoes and sprinkle over with the cheese, bake in a pre-heated oven at 180C until golden.
Serve with garden peas and vegetarian onion gravy.