Heat oil in a non-stick pan add onion and mushrooms. Sauté mushrooms for 1-2 minutes and season it with salt and black pepper powder.
In a bowl add sautéed mushrooms, garlic mayonnaise and coriander leaves. Mix well.
Break 2 eggs into a bowl add salt and black pepper. Beat with a fork and whisk until frothy.
Heat butter in a non-stick pan (medium flame). Pour the egg mixture in the heated pan and cook until the lower side is set.
Flip and cook from other side as well. Place mushroom stuffing in the centre of the omelette and fold it. Serve.