Pre-heat the oven to 350 degrees. Mist a 12-count standard-sized muffin tin with cooking spray.
Divide the torn spinach leaves, cherry tomatoes, crumbled Feta, and chopped basil evenly amongst the wells in the prepared muffin tin. You can layer the ingredients or mix them together, either way will work!
Crack the eggs into a large mixing bowl and add the milk, salt, pepper, oregano, and crushed red pepper. Beat with a whisk until well combined. Pour the egg mixture evenly over top of the fillings in each of the wells in the muffin tin.
Place the muffin tin in the oven and bake for about 20 minutes until puffy and set. Allow to cool for 10 minutes before removing from the muffin tin. I like to run a small spatula along the outside of each muffin before releasing it from the tin.