In a large saucepan, heat ½ teaspoon of coconut oil. Add the red chilies, coriander seeds, cumin, fenugreek, caraway or shahi jeera, cardamom, cloves, cinnamon, and peppercorns, and saute until they are fragrant and the coriander is slightly darker, 2-3 minutes. Add the poppy seeds, cashews, onions, ginger, and garlic, and continue to saute until the onions start to caramelize.
Remove the sauteed ingredients to a blender, add turmeric and paprika if using, vinegar, tamarind, and ½ cup of water, and blend into a smooth paste.
Heat the remaining 1 teaspoon oil in the same saucepan. Add the blended paste and mix well.
Cover the saucepan with a tight lid and let the paste cook for 20 minutes or until it turns a couple of shades darker. Stir occasionally to ensure it's not sticking to the bottom of the pan. If it is, add a little water.
After 20 minutes, add the mushrooms, potatoes and red peppers. Add some salt to taste, sugar, and cover again and let the stew cook another 15 minutes. The vegetables will release some juices, so don't add too much water at this stage. After 15 minutes, if the stew looks too thick, you can thin it out to your liking with vegetable stock or water.
Add the coconut milk and let it warm through. Garnish with coriander and serve hot with some rice or crusty bread.