Beat the eggs into a medium-sized bowl together with salt and black pepper.
In the same bowl, add in chopped mushrooms, chopped leeks, and bell pepper. Mix a bit to combine everything.
Preheat cast iron skillet and add in the butter used for cooking (or coconut oil). Make sure not to burn it by keeping the heat to medium temperature.
Once the butter (or coconut oil) is melted, add in the entire eggs mixture and cook gently on small to medium heat. Using a wooden or silicone spatula, stir from time to time making sure the eggs cook evenly.
When the eggs are cooked, remove from heat and set aside to cool down for 1-2 minutes.
Transfer to a plate and decorate with fresh herbs. Portion cooked eggs as needed, add the side veggies for each portion, and enjoy while still fresh and hot.