Preheat the oven to 190 degrees. Half your squash, scrape out the seeds with a spoon and cut into 4 or 6 pieces, depending on the size. Peel your sweet potato and cut into quarters. Put your squash and potato on the baking sheet, drizzle with a little bit of olive oil, salt and pepper and bake for about 30 minutes or till edges are browned and veggies get soft.
Peel and finely chop your onion and celery. Warm up 2 tbsp of oil the pot. Peel and grate or mince your ginger. When the oil is hot add onion with a pinch of salt and sautee on medium heat till translucent (about 5 minutes), then add celery and ginger. Keep sauteing and stirring for a couple of minutes for veggies to soften then add cumin, nigella and other whole spices if using. When spices start crackling (about 2 mins) add the rest of the spices and stir well.
Add lentils and stock, combine well and cover. Add some salt (depending on the saltiness of your stock). Check/ stir after 15 minutes and add more stock/water if the liquid is absorbed.
Get your squash and sweet potato out of the oven and cool for 10-15 minutes. When it is not too hot to handle peel and chop into bite-sized pieces. Mix into your curry. When the lentils are cooked add coconut milk. Mix thoroughly and reduce heat to low. Let the curry simmer with the milk for another 10 minutes.
Serve with rice or flatbreads, sprinkle with some pumpkin seeds and garnish with fresh coriander leaves before serving.