Preheat your oven to 400°F (200°C).
In a small oven-safe skillet or ceramic baking dish, combine the halved cherry tomatoes, diced red onion, and minced garlic.
Drizzle with the extra virgin olive oil and toss to coat evenly.
Roast the vegetables in the oven for 10-12 minutes until the tomatoes are blistered and the onions are tender.
Remove the skillet from the oven and stir in the fresh spinach, allowing the residual heat to wilt the leaves.
In a small bowl, whisk together the egg whites, sea salt, black pepper, and dried oregano.
Pour the egg white mixture over the roasted vegetables in the skillet.
Carefully crack the 3 whole eggs onto the surface of the mixture, spacing them out evenly.
Sprinkle the crumbled feta cheese over the top of the eggs and vegetables.
Return the skillet to the oven and bake for 8-10 minutes, or until the egg whites are fully set but the yolks are still slightly soft.
Remove from the oven and serve immediately with a dollop of plain Greek yogurt on the side for extra creaminess.