Chop onions, slit green chilies. Soak cashews for 15 minutes or wash green peas, drain them and set aside.
Heat oil in a pan, add cumin, mustard, allow them to splutter. Fry ginger garlic paste for 2 mins.
Add onions and fry them evenly till they brown, not burnt. While the onions fry, you can chop the mushrooms. Add tomato and saute until the moisture dries up and the raw smell goes off. Add chili powder, garam masala, curry leaves and turmeric. Saute until the raw smell has gone, just for a minute.
Wash mushrooms under running water, do not soak them in water for long as they tend to become soggy or soft.
Cut only before you add to the curry to avoid them from discoloring. Cut to desired sizes.
Add chopped mushrooms, cashews and salt. fry on a medium flame till you begin to get an aroma of mushrooms. This takes 2 mins.
Cover and cook on a low flame till the mushrooms are cooked, giving a good stir in between. Do not overcook as mushrooms tend to become soggy very fast. Add lemon juice if desired.