Boil the green peas in enough water. Strain and keep aside. Reserve the stock if using fresh peas.
Grind or blend the coconut and cashews with water to a fine smooth paste. Set aside.
Heat 1 tablespoon oil in a frying pan or skillet. Sauté chopped mushrooms in the oil for 5 to 6 minutes on medium to medium-high heat and then set aside.
In another pan, add 2 tablespoons oil. Add the mustard seeds and let them crackle.
Then add the cumin seeds, fenugreek seeds and urad dal.
Fry till the oil becomes aromatic and the dal gets golden. Don't over brown or burn the dal. Do this on a low or medium-low heat.
Now, add chopped onions. Sauté the onions stirring often till light golden.
Add the ginger-garlic paste or crushed ginger-garlic.
Fry till the raw aroma of the ginger-garlic goes away.
Now, add all the spice powders - coriander powder, red chili powder, turmeric powder and garam masala powder. Mix to combine.
Add chopped tomatoes. Sauté the mixture stirring often till the oil starts to leave its sides
Add the cashewnut-coconut paste and the curry leaves.
Mix and stir for 2 to 3 minutes. Add about 2 to 2.5 cups of the reserved green peas stock or water. You can add water less or more depending on the consistency you prefer.
Let the curry come to a boil and thicken slightly. Now, add the sautéed mushrooms and cooked green peas.
Add salt, stir and let the batani curry simmer further for 3 to 4 minutes more.
Serve the curry hot, garnished with some chopped coriander leaves.
Notes
Use fresh button mushrooms. Green peas can be fresh or frozen.