In a bowl, whisk the eggs together until well combined. Add the chopped onions, tomatoes, spinach, coriander, chilli, turmeric powder, garam masala powder, cumin powder, lemon juice, and salt to the beaten eggs and mix well until combined. Melt butter in a non-stick pan over a medium heat. Pour in half of the egg mixture. Swirl the eggs around for 2 minutes, pushing them to the middle, and tilting the pan so that the mixture sets well.

Cover with a lid and cook for a minute, then gently flip the omelete and cook uncovered. Once cooked on both sides, slip the omelete to your serving plate. Repeat the process for the remaining egg mixture. Serve hot with toasted bread or eat as is.