Rinse onions, bell peppers (optional) and green chilies (optional) under running water. Slice the onions and bell peppers thin. Fine chop green chilies and garlic.
Pluck and rinse coriander leaves in a bowl of water, a few times. Drain and fine chop. Set aside.
Remove long stems if any from the mushrooms. Rinse them under running water and slice them slightly thick, not too thin.
Break the eggs to a bowl and add salt, turmeric and pepper. Beat until frothy and keep aside.
Heat 1 teaspoon oil in a 6 inch pan. Add cumin, when they sputter, add garlic & green chili.
Saute them for 30 to 60 seconds. Then add onions, mushrooms & bell peppers(optional). Saute them on a slightly high heat until cooked and roasted.
Add coriander leaves. Mix and remove to a small plate.
To the same pan, add the rest of the oil and reduce the flame to medium. Pour the beaten eggs.
Cook until the eggs are almost set, yet slightly runny, spread the roasted onions and mushrooms. Flip and cook on the other side until eggs are cooked well. Remove to a serving plate and sprinkle dried herbs if desired.
Serve mushroom omelette hot with toasted bread or roll it in roti or tortilla. It also goes well as a side in any meal.