Dry roast all the spices except the red chillies and dry mango powder. Keep aside to cool. Roast the chillies separately taking care not to burn it. Cool and grind all the spices together. Mix in the dry mango powder and you have the achari spice blend.
In a pan, heat oil and sauté the chopped onions. Add the garlic and ginger and sauté till the onions are softened and turn light brown.
Meanwhile blanch and puree one tomato.
To the onions, add turmeric, Kashmiri chilli and achari spice blend. Saute on low flame for a minute and add the tomato puree. Continue to cook on low flame till the puree thickens and the gravy comes together.
Add the mushrooms and sauté for 2 minutes on high heat; season with salt. The mushrooms release a bit of water which helps to bring the dish together. Taste at this stage and adjust seasoning accordingly. Do not cook the mushrooms for too long; it should still have a bit to it when finished.
Take off flame and add the fenugreek leaves, lemon and coriander leaves.