Pre-heat oven to 180C
Place the olive oil in a pan and heat. Add the onions and sauté until soft and brown but not burned, then add the garlic, ginger and cook for 1 minute. Combine the spices and add the celery, tomatoes, tomato puree, tin of tomato, lentils, stock and leave it to simmer for 30 minutes. Stir one or twice to ensure the lentils don’t stick to the bottom of the pan. After 15 minutes add the coriander. Taste to season.
Skin the sweet potato, then cut into pieces and place in a steamer for about 10 minutes. Once cooked, add salt and pepper and mash well. Set aside. Place the lentil mixture in a baking dish, than cover with the mash potato, using a fork to layer it nicely. Sprinkle with salt, pepper and a drizzle of olive oil. Bake for 30 minutes.
Serve with a green salad tossed in a balsamic vinaigrette.
P.S. You can also use butternut squash for this dish as it works well too.