This is a very old friend - an adaptation of a Rose Elliottrecipe.
1/2 cup red lentils (125 ml by volume)
1 onion, peeled and chopped
300 ml water or (preferably) vegetable stock
1 tbs lemon juice
1/2 tsp Marmite or 2 tsp soya sauce
1/2 pack mushrooms, sliced
2 large tomatoes, peeled and sliced
2 slices wholemeal bread
60 g cheese
(optional) 1 tbs sesame seeds
Cook the lentils and the onions in the stock for 20 minutes, or until tender. Meanwhile put the sliced mushrooms and tomatoes in the bottom of an oven-proof casserole, and sprinkle with salt and pepper, and perhaps some herbes de provence. Whizz the bread and cheese together until breadcrumbed, and stir in the sesame seeds, if using.
When the lentils are cooked whizz with the lemon juice and Marmite/soya sauce, and any other seasonings you fancy. Pour this mixture over the top of the tomato/mushroom mixture, and top with the breadcrumbs/cheese. Bake in a moderate oven for about 40 minutes.
Serve with salad or a green vegetable or two, according to taste.