Crack the eggs into a small bowl. Add the milk (or water), dried oregano, a pinch of salt, and black pepper. Whisk vigorously with a fork until well combined and frothy.

Heat the olive oil in an 8-inch non-stick skillet over medium heat.

Add the halved cherry tomatoes and baby spinach to the skillet. Sauté for 1-2 minutes until the spinach is just wilted.

Pour the beaten egg mixture over the vegetables in the pan. Tilt the pan gently to ensure the eggs cover the bottom evenly.

Let the eggs cook undisturbed for about 30 seconds to set the base.

Using a heat-proof spatula, gently lift the edges of the omelet and tilt the pan to allow the uncooked liquid egg to flow underneath the cooked edges. Repeat this around the pan until no more liquid runs off freely.

Sprinkle the crumbled feta cheese over one half of the omelet.

Carefully fold the other half of the omelet over the cheese filling. Cook for another 30-60 seconds to warm the cheese through.

Slide the omelet onto a plate and serve immediately.