Preheat your air fryer to 149 °C (150 °C). Lightly grease a 7-inch round, oven-safe baking pan that fits comfortably in your air fryer basket.

In a medium bowl, whisk together the eggs, heavy cream, olive oil, oregano, salt, and pepper until well combined and slightly frothy.

Evenly distribute the chopped spinach, diced red bell pepper, sliced green onions, and crumbled feta cheese into the prepared baking pan.

Carefully pour the egg mixture over the vegetables and cheese in the pan. Gently stir with a fork to ensure the ingredients are evenly dispersed.

Place the pan into the preheated air fryer basket. Cook for 20-25 minutes, or until the frittata is set in the center and lightly golden on top. The exact time will vary depending on your air fryer model.

Using oven mitts, carefully remove the pan from the air fryer. Let the frittata rest for 5 minutes before slicing and serving.