Preheat your oven to 375°F (190°C) and spray a baking dish with nonstick cooking spray.

Boil the diced sweet potatoes in water for about 10 minutes until fork-tender. Drain and set aside.

In a skillet, sauté the chopped onion and spinach in olive oil over medium heat until tender (about 5 minutes).

In a large bowl, whisk together the eggs and milk. Stir in the sautéed vegetables, sweet potatoes, and cheese until well combined.

Pour the mixture into the prepared baking dish and bake for 30-35 minutes until set and golden brown.

Allow to cool for 5 minutes before slicing into squares. Serve warm.