Frittatas are the perfect meal for breakfast, lunch, and dinner!
Preheat the oven to 350 degrees Fahrenheit.
Chop and sautée the yellow onion in an oven safe skillet (8-9in.) with 1 tsp of olive oil.
Let the onions cook on low heat for 5-8 minutes.
Add the mushrooms and the second tsp of olive oil and cook for another 8 minutes.
Meanwhile, cut the spring onion into long strips.
Whisk the two eggs with the egg whites and pour the eggs into the skillet with onions and mushrooms.
Top the eggs with the strips of spring onions and add the feta.
Cook in the oven for 15-20 minutes, until the eggs are fully cooked.
Serve with a side of greens.