Preheat your oven to 375°F (190°C). Lightly grease a 9-inch pie dish.
In a medium bowl, whisk together the eggs, milk, garlic powder, salt, and pepper until well combined.
Stir in the shredded cheese, diced ham or mushrooms, tomatoes, and green onion.
Pour the mixture into the prepared pie dish and spread evenly.
Bake for 30–35 minutes, until the center is set and the top is lightly golden.
Let cool for a few minutes before slicing and serving.
