At first clean and wash the mushrooms very well and sliced it. Then chop the spinach leaves and wash it under the running water. Keep it aside.

Heat oil and butter in a pan and add onion. Over medium heat fry it till light brown in colour. Now add mushroom and give it a quick mix. Cook it 2-3 mins. When water is oozing out from mushroom then add spinach leaves. Stir it well.

Now add salt, chilli flakes and mixed herbs. Mix it well. Cook it till mushrooms are fully cooked. Now increase the heat and let any excess liquid evaporated from pan, then remove from the heat. Keep it aside.

Now break eggs into a large mixing bowl. Beat eggs really well. Add mushroom spinach mixture and half of cheese. Stir it to incorporate everything well. Now add rest of cheese and sprinkle black pepper powder. Do not mix it.

Transfer the mixture to oven-safe casserole. Preheat the oven to 180-degree celcius or 350-degree Fahrenheit. Put the casserole into the oven and bake it for 15 mins or until the eggs are completely cooked in the center of the casserole.

Remove it from oven. Allow it to little cool down. Cut it in triangle shape or whatever shape you like and serve it.