Preheat the oven to 350°F or 180°C.
Lightly grease a muffin tin with the olive oil.
In a deep mixing bowl, whisk together the eggs until smooth. Season to taste and add the fresh herbs if using.
Stir in the chopped spinach and crumbled cheese and mix well until fully combined.
Pour the mixture into the muffin tin. Be careful to only fill each cup half way, as you will need to leave room for the muffins to expand as they’re cooking.
Place in the oven for 15-18 minutes, until the egg is fully set and the muffins are lightly golden brown.
Leave the muffins to cool slightly and then turn the tin over to allow them to pop out. Serve immediately or refrigerate for later use.
