Preheat the oven to 400 degrees F. Lightly coat two 6-ounce ramekins with cooking spray.

Heat the olive oil in a medium saucepan set over medium heat.

Add the onion and cook until softened and just starting to brown, 5 to 6 minutes. Add the zucchini and cook for 2 additional minutes.

Divide the vegetable mixture evenly between the two ramekins. Top with the Gruyere cheese.

In a small bowl, whisk together the eggs, egg white and water. Pour the mixture over the vegetables in the ramekins. Season with salt and pepper.

Place the ramekins on a baking sheet and transfer to the oven.

Bake until the eggs are set and just starting to brown, about 20 minutes.

Garnish with parsley. Serve.