Peel and finely dice the garlic and place on a pan greased with a tablespoon of ghee. Season with salt and cook over a medium-high heat for just a minute until fragrant. Add the sliced mushrooms and cook for 5 minutes until lightly browned stirring occasionally.
Add the spinach and cook until wilted for just a minute or two (squeeze out the water if using frozen and thawed spinach). Take off the heat and place in a bowl. Discard the excess liquids before using the pan for cooking the omelet.
Crack the eggs into a bowl and mix using a fork. Season with salt and pepper to taste.
Pour the eggs evenly in a hot pan greased with a tablespoon of ghee. Use a spatula to bring in the egg from the sides towards to centre for the first 30 seconds. Lower the heat and cook for another minute. When the top is almost cooked, add the spinach and mushroom topping and crumbled feta. Fold the omelet in half, cook for another minute just to warm up the topping.