Preheat the air fryer to 360°F (182°C).
Spray a small, air fryer–safe pan with nonstick cooking spray and set aside.
In a medium bowl, crack and beat 4 large eggs until blended. Season with salt and black pepper to taste.
Stir 1/4 cup diced bell peppers, 1/4 cup chopped spinach, and 1/4 cup shredded low-fat cheese into the beaten eggs until evenly combined.
Pour the egg mixture into the prepared pan and smooth the top gently.
Place the pan in the air fryer basket and cook at 360°F for 5–7 minutes, or until the omelet is set, puffed, and no longer runny in the center.
Using oven mitts, remove the pan from the air fryer. Run a butter knife around the rim to loosen the omelet, then invert the pan onto a plate to release the omelet.
Serve immediately.