Preheat oven to 350 degrees.
Grease 9 x 13 pan or 8 x 8 square pan if thicker squares desired.
Sauté onion and spinach in pan with oil and salt until spinach shrinks to half or less its original size.
Add Italian Seasoning and stir (if you can’t get ground, okay to use dried).
Set spinach mixture aside to cool.
In separate bowl, whisk together eggs and milk.
Add spinach to eggs and mix together.
Pour into cooking pan, sprinkle top with grated or shredded cheese and bake in oven for 45 minutes until top is brown (If using 8 x 8 pan, may need to let center cook longer).
Let cool slightly, 10-15 minutes.
Cut into squares and serve!