Preheat oven to 350˚F. Heat olive oil in a large ovenproof skillet over medium high heat.
Add the red onion and cook for 3-4 minutes until somewhat softened. Stir in garlic and spinach, cooking for 1 more minute until garlic is fragrant.
Add zucchini, tomatoes, asparagus, olives, oregano, salt and pepper. Mix completely. Lower heat to medium. Add mushrooms last.
In a large bowl, whisk eggs together with milk and feta cheese. Add the egg mixture to the pan and cook for about 3 minutes, until the sides are set.
Top with an extra pinch of pepper. Place the pan on a middle rack in the oven and bake for 20 minutes, or until the middle is set. Garnish with any extra oregano and feta cheese. Serve immediately. Good paired with lightly dressed spring mix!
