Add oil to a heavy bottomed pot or kadai. Allow it to heat up on a medium high flame. Once hot add mustard seeds and cumin seeds and sauté for 10-15 seconds till they start spluttering. Add curry leaves and fry lightly for a few seconds.
Now add onions and ginger garlic paste. Sauté till the onions are translucent. Add the tomatoes, turmeric powder, cumin powder, salt and chilli powder and fry the masala for a minute or two on medium high heat. Keep adding 1/4-1/2 cup water as you fry the masala.
Add green chillies and cover and cook for 5-7 minutes.
While the gravy is cooking, boil green peas in water for 2-3 minutes and set aside
Add mushroom and cook for 1-2 minutes or until mushrooms are firm and tender. Add the remaining water and green peas.
Add garam masala and salt and stir to combine. Once done, sprinkle roasted kasuri methi and coriander leaves. Serve hot!