Heat oil in a pan over medium heat.
Add sliced onions and green chillies, sauté until onions are golden brown.
Stir in ginger-garlic paste and cook for a minute until fragrant.
Add turmeric powder, red chilli powder, and salt; mix well.
Add sliced mushrooms and cook until they release water and become tender, about 10 minutes.
Sprinkle garam masala and mix well.
Cook for another 2–3 minutes until the spices are well incorporated.
Remove from heat and garnish with fresh coriander leaves and lemon juice if using.
Serve hot with rice or roti.