Grind together coconut and cashew nuts to a smooth paste with required amount of water.
In a deep bottomed vessel, heat oil and add mustard seeds and cumin seeds and let them splutter.
Add the onion and fry until brown. Add the ginger garlic paste and mix.
Add the ground tomato with turmeric, coriander powder, cumin powder and Garam masala and cook until the oil oozes out on the sides.
Add the mushrooms and sauté them for 5 minutes.
Add the coconut Cahewnuts paste, salt and water and simmer underlid until the mushrooms are cooked.
Garnish with coriander leaves.