Preheat oven to 350 degrees.
Lightly grease a muffin tin with cooking spray or olive oil and set aside.
Crack eggs into a mixing bowl.
Add milk, olive oil, and Cavender's Greek Seasoning.
Whisk until smooth and evenly combined.
Fold chopped spinach into the egg mixture.
Add crumbled feta and mix gently to distribute.
Divide the mixture evenly into the muffin tin.
Fill each muffin cup about 3/4 full.
Top with extra feta if desired.
Bake for 18 to 22 minutes until the egg cups are set, lightly puffed, and soft in the center.
Allow egg cups to rest for 5 minutes.
Remove carefully and place on a cooling rack.
Serve warm or refrigerate for meal prep.