Preheat the oven to 350 degrees F. Lightly grease a 9x13 casserole dish with butter or oil.
In a medium mixing bowl, whisk together the eggs, milk, and seasonings, until combined.
In a large saute pan, heat oil and saute onions and tomatoes until soft. Add spinach and cook while stirring, until spinach is wilted. Pour into prepared casserole dish.
Pour the egg mixture over the vegetables and sprinkle with cheese. Cover with foil and bake for 25-30 minutes or until eggs are set and cheese is melted. Serve and enjoy!
