Preheat the oven to 375°F (190°C).
Lightly grease a 12-cup muffin pan with nonstick cooking spray.
Steam or microwave the broccoli for 2 to 3 minutes until just tender. Let it cool slightly.
In a large bowl, whisk together the eggs, milk, garlic powder, onion powder, salt, and black pepper.
Stir in the broccoli, shredded cheddar cheese, diced onion, and chives.
Evenly divide the mixture among the prepared muffin cups, filling each about three-quarters full.
Bake for 18 to 22 minutes, or until the centers are set and the tops are lightly golden.
Allow the muffins to cool in the pan for 5 minutes before removing.
Serve warm or let cool completely for meal prep.