In a shallow dish, whisk together egg whites (or protein powder), milk, egg, cinnamon, vanilla extract, and salt until well combined.
Dip each slice of bread into the egg mixture, ensuring both sides are coated.
Heat a lightly oiled or buttered skillet over medium heat.
Cook the French toast for 3-4 minutes per side, until golden brown and cooked through.
Alternatively, for air fryer method: Preheat air fryer to 375°F (190°C). Lightly spray basket with cooking spray. Place coated bread in a single layer and cook for 5-7 minutes, flipping halfway through, until golden.
Serve immediately with your favorite toppings.
Notes
For a thicker batter, add a little more protein powder or reduce milk slightly.
Use whole wheat or sourdough bread for added fiber.