01 - Set oven to 375°F (190°C) and allow to preheat completely.
02 - Coat a medium oven-safe skillet or baking dish with 1 tablespoon olive oil. Add spinach, cherry tomatoes, onion if using, and garlic. Season lightly with salt and black pepper. Toss until well combined.
03 - Distribute the crumbled feta cheese evenly across the vegetable mixture.
04 - Drizzle the remaining 1 tablespoon olive oil over the top and sprinkle with dried oregano or Italian herb mix. Add chili flakes if desired.
05 - Create four small wells in the mixture and gently crack one egg into each well.
06 - Transfer the pan to the oven and bake for 15 to 20 minutes, until egg whites are set and yolks remain slightly runny.
07 - Remove from oven, let cool slightly, and serve warm.