Preheat your oven to 350°F (177°C).

In a large bowl, whisk the eggs with the Greek seasoning, salt, and pepper until light and airy.

Heat the olive oil in a skillet over medium heat. Add the chopped onion and cook until softened.

Stir in the spinach and cook until it wilts down.

Add the cherry tomatoes and garlic, sautéing for about a minute until fragrant.

Coat a muffin tin with nonstick spray and divide the vegetable mixture evenly among the cups.

Pour the egg mixture over the vegetables, filling each cup halfway to two-thirds full.

Sprinkle crumbled feta onto the top of each cup.

Bake for 30 minutes, or until the egg cups are set and fully cooked.

Let them rest for 5 minutes before serving.