Preheat oven to 375 degrees F. Whisk together the whole eggs, egg whites, salt, pepper, and nutmeg.
In a small skillet over medium heat, add oil. Add onion and spinach and sauté 3-5 minutes.
Add the egg mixture and quickly scrape all sides of pan to evenly distribute egg and veggies. Remove from heat and place in the oven for 10 minutes until egg is fully cooked.