Making Cashew Paste: Soak 10-12 cashews in hot water for 10 to 15 minutes. Then puree in a blender to a smooth paste along with ¼ cup water. Keep it aside.
Add diced onions, tomatoes, ginger, garlic, and green chili in a blender and blend without adding water to make a smooth puree. Keep it aside.
Press SAUTE mode on Instant Pot. Heat oil, add cumin seeds, and let them splutter.Next, add the pureed onion-tomato mixture, and cook for around 3-4 minutes until the raw smell disappears. Then add all the dry spices like turmeric, red chili powder, coriander powder, garam masala, and salt. Stir to combine. Scrape the bottom and deglaze the pot. This step is crucial to ensure you don't get the burn notice when you pressure cook. Add in the sliced mushrooms, peas, and water. Combine gently with the masala.Note: You can also use do Pot-in-Pot Cooking or PIP. This means you can cook multiple things at the same time. Place the trivet and then the bowl of basmati rice with water. This way, they will both curry and rice will cook together. Close the lid securely, and turn the vent to "SEALING". Select the PRESSURE COOK/MANUAL (High Pressure) setting and set the cooking time to 4 minutes.
When the pot beeps, Do a Quick pressure release before opening the lid.
Then add cashew cream, crushed Kasuri methi, coriander leaves, lemon juice, and mix well. Simmer the curry for 2 to 3 minutes, and the curry will thicken.
Mushroom Masala is ready, serve with naan, chapatis, roti or hot basmati rice.