Prepare Oven: Set your oven to preheat to 375°F (190°C). Ensure an oven rack is positioned in the center.

Whisk Eggs: In a spacious mixing bowl, vigorously beat the eggs with the ground black pepper, salt, and dried oregano until the mixture is well combined and slightly frothy.

Sauté Aromatics and Spinach: Place the 10-inch oven-safe nonstick skillet over medium heat. Add the extra-virgin olive oil. Once the oil is shimmering lightly, introduce the minced garlic and cook for about 30 seconds until fragrant, being careful not to let it brown. Add the chopped baby spinach to the skillet. Gently stir and cook until the spinach has fully wilted down, which should take approximately 4-5 minutes.

Combine and Cook Base: Pour the seasoned egg mixture evenly over the wilted spinach directly in the skillet. Scatter the crumbled feta cheese uniformly over the top of the egg mixture.

Bake Frittata: Carefully transfer the skillet to the preheated oven. Bake for 14-18 minutes, or until the frittata is puffed, appears golden at the edges, and the center is just firm to the touch when gently pressed.

Rest and Serve: Remove the frittata from the oven and allow it to rest in the skillet for a few minutes. This helps it set further and makes slicing easier. Cut into wedges and serve warm.