Wash and cut button mushrooms into bite-size pieces.
Heat oil in a pan, add sliced onions. Saute onions for 3 minutes.
Add ginger, garlic and green chillies.
Cook onions till they are dark golden brown in colour. Make sure not to burn them. Keep the flame medium to high.
Transfer the onions to a plate and keep aside to cool down.
Once cooled, transfer them into a blender and using half cup water blend the onions to a fine paste.
Onion masala for mushroom curry is ready.
Heat 2 tablespoons of oil. Add chopped tomatoes.
Cook tomatoes till they soften. Slightly mash them using the back side of the spatula.
Add the onion paste and saute for 5-7 minutes oil separates from the masala.
Add coriander powder, garam masala powder, red chilli powder and turmeric powder. Add salt to taste.
Mix spices with the masala and cook for another 2 minutes.
Add the chopped mushrooms and mix.
Add hot boiling water for the gravy.
At first, add little water as mushrooms tend to release their water.
Later, add water as per the gravy you prefer. Cover & cook mushrooms till they soften.
Lastly, garnish with fresh coriander leaves. Mushroom Masala is ready.
Serve hot with roti, partha or jeera rice.