Place the pie crust in a pie dish and crimp the edges if needed.
Heat a small skillet over medium heat. Add the broccoli florets and diced onion, then sauté for 4-5 minutes, until the onion is softened and the broccoli is slightly tender.
Add the sautéed broccoli and onion to the prepared pie crust.
Sprinkle the shredded cheddar cheese evenly over the broccoli and onion.
In a large bowl, whisk together the eggs, milk, salt, garlic powder, and pepper until smooth.
Pour the egg mixture evenly over the broccoli, onion, and cheese.
Bake for 40-45 minutes, or until the center is set and the top is lightly golden.
Let the quiche cool for 10 minutes before slicing and serving.