Preheat your air fryer to 350°F (175°C) for a few minutes.
In a large bowl, whisk together the 6 large eggs, 1/4 cup milk, 1/4 cup Parmesan cheese, 1/4 tsp garlic powder, 1/4 tsp dried oregano, Salt and pepper until smooth.
Fold in the 1/2 cup cherry tomatoes, 1/2 cup spinach, diced 1/4 cup onion, and chopped 1/4 cup bell peppers.
Lightly spray a small, air fryer-safe pan or dish with non-stick cooking spray.
Pour the egg and veggie mixture into the prepared pan and place it in the air fryer basket. Cook for 15–18 minutes.
About 2 minutes before the cooking time ends, sprinkle 1/4 cup shredded mozzarella cheese evenly over the top.
Test doneness by inserting a toothpick into the center — it should come out clean.
Let the frittata rest for 2–3 minutes, then slice and serve warm.